Published for SISSA by Springer Received: March 6, 2019 Accepted: May 9, 2019 Published: May 23, 2019 Constraints on mediator-based dark matter and scalar √ dark energy models using s = 13 TeV pp collision JHEP05(2019)142 data collected by the ATLAS detector The ATLAS collaboration E-mail: atlas.publications@cern.ch Abstract: Constraints on selected mediator-based dark matter models and a scalar dark √ energy model using up to 37 fb−1 s = 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015–2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin- 1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators √ embedded in extended Higgs sector models. In this case, also s = 8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy). Keywords: Dark matter, Hadron-Hadron scattering (experiments) ArXiv ePrint: 1903.01400 Open Access, Copyright CERN, https://doi.org/10.1007/JHEP05(2019)142 for the benefit of the ATLAS Collaboration. Article funded by SCOAP3 . Contents 1 Introduction 1 2 Theoretical framework 2 2.1 Vector or axial-vector dark matter models 3 2.1.1 Neutral interaction 3 2.1.2 Baryon-number-charged interaction 5 JHEP05(2019)142 2.1.3 Flavour-changing interaction 5 2.2 Scalar or pseudo-scalar dark matter models 6 2.2.1 Colour-neutral interaction 6 2.2.2 Colour-charged interaction 7 2.3 Extended Higgs sector dark matter models 8 2.3.1 Two-Higgs-doublet models with a vector mediator 9 2.3.2 Two-Higgs-doublet models with a pseudo-scalar mediator 9 2.4 EFT model of scalar dark energy 10 3 Dataset and signal simulation 12 4 Experimental signatures 13 4.1 Searches for invisible final states 14 4.2 Searches for visible final states 18 4.3 Complementarity and combination of signatures 23 5 Systematic uncertainties 24 6 Interpretation of the results 25 6.1 Vector or axial-vector dark matter models 26 6.1.1 Neutral interaction 26 6.1.2 Baryon-charged interaction 32 6.1.3 Neutral flavour-changing interaction 33 6.2 Scalar or pseudo-scalar dark matter models 34 6.2.1 Colour-neutral interaction 34 6.2.2 Colour-charged interaction 37 6.3 Extended Higgs sector dark matter models 37 6.3.1 Two-Higgs-doublet models with a vector mediator 37 6.3.2 Two-Higgs-doublet models with a pseudo-scalar mediator 38 6.4 Scalar dark energy model 43 7 Conclusions 44 –i– A Signal models generation details 46 A.1 V/AV models 46 A.2 VFC model 47 A.3 2HDM + a models with heavy-flavour final states 48 B Comparison with direct and indirect searches 49 The ATLAS collaboration 69 JHEP05(2019)142 1 Introduction The existence of a non-luminous component of matter and the origin of the accelerating expansion of the universe are two major unknowns in our current understanding of the universe. The existence of dark matter (DM) is supported by a variety of astrophysical measure- ments, ranging from the rotational speed of stars in galaxies, over precision measurements of the cosmic microwave background [1, 2], to gravitational lensing measurements [3–5]. How- ever, the nature and properties of the DM remain largely unknown. Searches for particle DM are performed using different complementary approaches: the measurement of elastic scattering of DM by nuclei and electrons in a detector [6–14], the detection of Standard Model (SM) particles produced in the annihilations or decays of DM in the universe [15– 19], the production of DM particles at colliders [20–38], and the study of the effect of DM interactions on astrophysical systems [39, 40]. Another major unknown in the physics of our universe, beside the nature of DM, is the origin of its accelerating expansion [41, 42]. In the context of a homogeneous and isotropic universe, this implies the existence of a repulsive force, which causes the universe to expand at an accelerating rate [43]. Assuming general relativity, one of the simplest explanation for this repulsive force is a new type of matter which mimics a constant energy density, thus dubbed dark energy (DE). The effect of DE on cosmological scales is studied by measuring the redshift-distance relation using supernovae, baryon acoustic oscillations, the matter power spectrum and the cosmic microwave background, as well as gravitational lensing [44]. On microscopic scales, DE is probed by laboratory experiments searching for additional gravitational forces that would lead to deviations from the 1/r2 law [45–53]. Multi-messenger astronomical observations also provide important information for understanding the nature of DE [54–56]. The work reported in this paper considers the hypothesis that the DM is composed of a weakly interacting massive particle (WIMP) [57]. WIMPs can account for the relic density of non-relativistic matter in the early universe [58] measured in data from the Planck [2] and WMAP [1] experiments. For benchmarking purposes it is assumed that WIMPs are Dirac fermions in all models evaluated in this paper. Theories such as R-parity-conserving supersymmetry [59–62] can also provide such WIMP DM candidates. These models are examined using a wide range of experimental signatures [63–73] in searches performed by the ATLAS and CMS Collaborations. These searches are not included in this paper. –1– For most of the models in this paper, WIMPs are potentially pair-produced in pp collisions at the Large Hadron Collider (LHC) [74]. These particles, denoted by the symbol χ throughout this paper, are stable over cosmological scales and do not interact with the detector. To identify events with DM, additional particle(s), X = jet, γ, W, Z, h, (t)t̄, (b)b̄, need to be produced in association with DM in a pp collision, in order to tag the event and detect the recoiling WIMPs as missing transverse momentum (with magnitude ET miss ). If the DM candidates can be produced at the LHC via an s-channel exchange of a new particle, then this mediator could also decay back into SM final states: resonance searches can therefore also be used to constrain DM models. The interplay of resonance and X + ET miss searches depends on the specific model choice and is further outlined in this paper. In the JHEP05(2019)142 models under study, some of which are new with respect to previous ATLAS publications, one or more new particles mediate the interaction of DM with the SM particles. The first category considers simplified models mediated by a vector, axial-vector, scalar or pseudo-scalar mediator. In the case of simplified vector and scalar mediators, different types of interactions are explored (baryon-charged, neutral-flavour-changing and coloured interactions). The second category considers less simplified models involving an extended Higgs sector plus an additional mediator, either a vector or a pseudo-scalar particle. The assumptions and choices of the models closely follow the work of the DM Forum/LHC DM Working Group [75–78]. Analyses focusing on signatures compatible with (unstable) long- lived particles decaying in the detector volume are also not considered in this paper [79]. Results from particle physics experiments may be used to elucidate the microscopic nature of DE [80, 81]. Hadron collider data considering X + ET miss final states are used to constrain Horndeski models of DE [82] in an effective field theory (EFT) framework [83]. This paper aims to provide an overview of the experimental programme of ATLAS searches [84] for mediator-based DM production performed to date using 13 TeV proton- proton collisions delivered by the LHC in 2015 and 2016. The studies presented in this paper use public ATLAS results. Since no significant excess over the expected SM background was found in any of these analyses, the results are used to constrain the available phase space for DM models. Furthermore, DE models are also constrained using these analyses. The paper is structured as follows. The DM and DE models evaluated in this paper are outlined in section 2, while the data and simulation samples are described in section 3. The data analyses for each different signature are briefly described in section 4, where the complementarity of different final states is also discussed. Finally, the dominant systematic uncertainties affecting the modelling of the signal samples are highlighted in section 5 and the results are presented in section 6, followed by the conclusions (section 7). 2 Theoretical framework All DM results presented in this paper are interpreted in the framework of simplified DM models [75, 78, 85–88], where a new particle (or set of particles) mediates the interaction of DM with the SM particles. These DM simplified models, which overcome some of the shortcomings of previous EFT-based DM models [87, 89–93], can be classified according to content and properties of the particles that mediate the interaction between DM and –2– SM particles (mediator sector), giving rise to collider signatures with different kinematic characteristics and topologies. Two classes of models are taken into account: the case where the mediator sector is composed of a single particle, either of spin-1 (section 2.1) or of spin-0 (section 2.2), and the case where the mediator sector is composed of an extended Higgs sector plus an additional mediator, either a spin-1 (section 2.3.1) or spin-0 (section 2.3.2) particle. Finally, a Horndeski model of DE [94] is studied within an EFT framework and is used to interpret the results (section 2.4). All models described in this section are summarised in table 1. For all models, the JHEP05(2019)142 width of the mediator is always assumed to be the smallest width that can be calculated from all other parameters [75] (minimal width assumption). Furthermore this paper as- sumes DM to be a Dirac fermion.1 2.1 Vector or axial-vector dark matter models The first category of models under study in this paper consists of a set of simplified models with a single spin-1 particle that acts as the mediator. This category of models that assume the existence of new gauge symmetries is among the most commonly studied extensions of the SM [95] and provides a convenient framework to describe the interaction between the SM and DM. Three types of simplified models involving a single spin-1 particle are investigated: a neutral mediator [93, 96–102], a baryon-number charged mediator [103– 106] and a flavour-changing neutral-current mediator [107–109]. 2.1.1 Neutral interaction One vector or axial-vector simplified model (V/AV) [75] consists of a simple extension of the SM with an additional U(1) gauge symmetry under which the DM particles are charged. The new mediator (Z 0 ) is either a vector (ZV 0 ) or an axial-vector (Z 0 ) boson. The model A has five parameters [75]: the masses of the mediator and the DM particle (mZ 0 and mχ , V/A respectively), the flavour-universal coupling of the Z 0 boson to all flavour quarks, gq ; the coupling to all lepton flavours, g` ; and the coupling to DM, gχ . Representative diagrams for this model are shown in figure 1. The Z 0 mediator can decay into a pair of quarks, a pair of leptons, or a pair of DM particles. In the latter case, an additional visible object has to be produced in association with the mediator as initial-state radiation (ISR), as shown in figure 1a. The visible object can either be a jet, a photon or a W or Z boson. In order to highlight the complementarity of dedicated searches based on different final states [77], two coupling scenarios, a leptophobic and a leptophilic Z 0 mediator, respectively, are considered for the interpretation of these models (see section 6.1.1). 1 The alternative assumption that DM is a Majorana fermion changes not only the set of allowed inter- actions, but also the total cross-section for the ones that are allowed. Aside from these, changing the choice of Dirac fermions, Majorana fermions, or scalars is expected to produce minor changes in the kinematic distributions of the visible particles in the final state. However, these assumptions have not been evaluated further in terms of simplified DM models [75]. –3– Short description Acronym Symbol J P Charge Signatures Results (Section 4) Section: 0 0 ∓ miss Vector/axial-vector V/AV ZV /ZA 1 × jet/γ/W /Z+ET , 6.1.1 mediator difermion resonance Vector VBC ZB0 1− baryon-number miss h + ET 6.1.2 baryon-number-charged mediator 0 1− flavour miss JHEP05(2019)142 Vector flavour-changing VFC ZVFC tt, t + ET 6.1.3 mediator Scalar/pseudo-scalar S/PS φ/a 0± × jet+ET miss , 6.2.1 miss mediator tt̄/bb̄+ET Scalar colour-charged SCCq/b/t ηq/b/t 0+ colour, 2/3 jet+ETmiss , 6.2.2 miss miss mediator electric-charge b + ET , t + ET 0 0 Two-Higgs-doublet plus 2HDM+ZV ZV 1− × miss h + ET 6.3.1 vector mediator Two-Higgs-doublet plus 2HDM+a a 0− × W/Z/h + ET miss , 6.3.2 miss pseudo-scalar mediator tt̄/bb̄+ET , h(inv), tt̄tt̄ Dark energy DE φDE 0+ × jet+ET miss , tt̄ 6.4 miss +ET Table 1. Summary of the mediator-based simplified models considered in this paper, along with the associated model acronym (2nd column, defined in the text) and mediator symbol (3rd column) used throughout. The 4th and 5th columns indicate the quantum numbers of the mediator. The ‘×’ indicates the cases where no other charge than the new mediator’s interaction is present. The 6th column indicates the final-state signatures (details in section 4) and the 7th column gives the reference to the interpretation. q̄ γ/V /g χ q̄ f 0 0 ZV/A ZV/A q χ̄ q f¯ (a) (b) Figure 1. Schematic representation of the dominant production and decay modes for the V/AV model. –4– q̄ h u t g ū u t u ZB0 χ u 0 ZVFC 0 ZB χ/t t 0 ZVFC 0 ZVFC q χ̄ g χ̄/ū u t u t (a) (b) (c) (d) Figure 2. Schematic representation of the dominant production and decay modes for the (a) VBC JHEP05(2019)142 model and (b,c,d) VFC model. 2.1.2 Baryon-number-charged interaction The baryon-number-charged mediator simplified model [75, 106] (VBC) considers a spin-1 vector mediator. It also assumes that the charge of the U(1) symmetry coincides with the baryon number and it is spontaneously broken by a baryonic Higgs scalar. The DM candi- date in this model is a stable baryonic state and it is neutral under the SM gauge symmetry. While the model can provide an ISR signature through s-channel ZB0 -mediator production subsequently decaying into a pair of DM candidates as for the V/AV models described in the previous section (figure 1a), it can also exhibit a distinctive h + ET miss signature [106], as shown in figure 2a. The model has five parameters [106], whose values are chosen to enhance the cross-section for h + ET miss final states relative to traditional ISR signatures. The mixing angle between the baryonic and the SM Higgs bosons, θ, is fixed to sin θ = 0.3 in order to comply with the current Higgs boson coupling measurements. The coupling of the mediator ZB0 with the quarks, gq , and the DM, gχ , are set to 1/3 and 1, respectively. The coupling of the mediator with the Higgs boson, gZB0 , is set to the ratio of the mediator mass to the vacuum expectation value (VEV) of the baryonic Higgs boson: mZB0 /vB . The mediator is naturally leptophobic, thus evading the current constraints coming from the dilepton resonance searches. Different mediator and DM masses are investigated. 2.1.3 Flavour-changing interaction The flavour-changing vector mediator model (VFC) [109] permits the interaction of the DM candidate with the top quark. A spin-1 colour-neutral mediator ZVFC 0 enables a flavour- changing interaction of the DM with ordinary matter, for instance between the top quark and the up quark. For simplicity, the mediator is allowed to couple only to the right-handed component of the top-quark field [109]. This model predicts flavour-changing neutral cur- rent (FCNC) processes which are suppressed in the SM. A representative diagram of the on-shell production of the new mediator ZVFC 0 is shown in figure 2b. The mediator can either decay invisibly, leading to a final state involving a single top quark and large miss- ing transverse momentum, or decay visibly, producing a distinctive final state containing two top quarks with the same electric charge (tt/t̄t̄). A similar topology arises from the t-channel exchange of the ZVFC0 mediator, as depicted in figures 2c and 2d. –5– g g g g t χ φ/a t Z/γ/g/h t t b/t φ/a χ̄ t t t t̄ χ b̄/t̄ t̄ t̄ φ/a g g χ̄ g (a) (b) (c) JHEP05(2019)142 g b/t q̄ q̄ b W− χ/b/t χ χ W a φ/a a χ̄/b̄/t̄ χ̄ χ̄ g b̄/t̄ b t g t (d) (e) (f ) Figure 3. Schematic representation of the dominant production and decay modes for the S/PS models. The model is fully predictive once the four main parameters are specified [110]: the mass of the mediator mZVFC 0 , the DM mass mχ , and the couplings of the mediator to the DM particles and to the quarks, gχ and gut , respectively. In the context of the analyses described in this paper, the mass of the DM candidate mχ has negligible impact on the kinematics, provided that mZVFC 0 > 2mχ , and it is fixed to 1 GeV. This reduces the number of dimensions of the parameter space to three. The sensitivity of the experimental analyses to this model is explored in three scenarios that investigate different parameter planes as a function of mZVFC 0 0 , gut and the invisible branching ratio of the ZVFC mediator, B(χχ̄). 2.2 Scalar or pseudo-scalar dark matter models The second category of models under study in this paper consists of a set of simplified models with a single spin-0 particle that composes the mediator sector. In simplified models the mediator couples to SM fermions proportionally to the Higgs Yukawa couplings. These models can therefore be easily included in the extended Higgs boson sectors of ultraviolet-complete (UV-complete) theories. The various models can be grouped in two broad categories: colour-neutral [111–120] or colour-charged mediators [107–109, 121–135]. The latter category is divided into three further models with different final states. 2.2.1 Colour-neutral interaction In the scalar or pseudo-scalar simplified models (S/PS) a new spin-0 gauge particle mediates the interaction, at tree level, with a DM particle [75, 113]. The mediator is considered to be either a scalar (φ) or a pseudo-scalar (a). This model has four parameters [25]: the mass of –6– the mediator mφ or ma ; the DM mass; the DM-mediator coupling, gχ ; and the coupling of the mediator with the SM fermions. The latter is composed of a flavour-universal term, gq , which is a free parameter of the model and multiplies the SM-Yukawa coupling for each of the fermions [113]. This particular form of interaction, common to all models with spin-0 mediators evaluated in this paper, is typically referred to as the minimal flavour violation (MFV) ansatz and by construction, it relaxes the severe restrictions on the coupling of new spin-0 colour-neutral particles to the SM fermions imposed by flavour measurements [136– 138]. Furthermore, it implies that these mediators are sizeably produced through loop- induced gluon fusion or in association with heavy-flavour quarks (see figure 3). According to whether the mediator decays into a pair of DM or SM particles, different final states JHEP05(2019)142 are sensitive to these models. Due to the Yukawa-like structure of the couplings, visible final states with two or four top quarks are particularly important signatures. Final states involving a single top quark and ET miss may also play an important role in constraining these models [139–144]. Despite the absence of a dedicated parameter that regulates the relative importance of up-type and down-type quark couplings (otherwise present in UV completions of these models as in section 2.3.2), it is also important to study final states involving bottom quarks separately, since these become a relevant signature if the up-type couplings are suppressed. 2.2.2 Colour-charged interaction The scalar colour-charged interaction model (SCC) assumes that the scalar mediator cou- ples to left- or right-handed quarks and it is a colour triplet. The DM particle(s) is produced via a t-channel exchange of the mediator which leads to a different phenomenology from that of colour-neutral interactions. These models have a strong connection with the mini- mal supersymmetric Standard Model (MSSM) [145, 146] with a neutralino DM and first- and second-generation squarks with universal masses. They share with it the same cross- sections and phenomenology when the mediator is pair-produced via strong interaction. Nevertheless, additional production diagrams are taken into account in this scenario, since values assumed for the couplings of the mediator to quarks and DM differ from those of the MSSM. As in the case of the MSSM, it is reasonable to decouple the first two generations from the third, considering the different mass scales. For this purpose, three different models are considered:2 1. In the SCCq model, the mediator, ηq , couples to the left-handed quarks of the first and second generations and is a SU(2) singlet under the SM. The mediator decays into a quark-DM pair, so that the strongest sensitivity for these models is provided by searches involving jets and missing transverse momentum. The three model pa- rameters are the mediator mass, the DM mass, and the flavour-universal coupling to quarks and DM, λq . This model is described in detail in refs. [26, 101] and represen- tative diagrams are shown in figures 4a, 4b and 4c. 2 These three scenarios provide benchmarks for each signature considered and do not aim to be an exhaustive set of models involving colour-charged interactions. –7– γ/V /g q χ q/b d¯ t χ q/b χ q/b ηq /ηb ηq ηq /ηb χ̄ q/b ηq /ηb ηt q̄ χ̄ g g q/b s χ̄ χ̄ (a) (b) (c) (d) Figure 4. Schematic representation of the dominant production and decay modes for the SCC JHEP05(2019)142 models. 2. In the SCCb model, the mediator, ηb , couples to the right-handed bottom quark. Following previous publications [25, 147], the specific realisation of this model is obtained within the framework of “flavoured” DM, where the DM candidate is the lightest component of a flavour triplet [131]. With these assumptions, the mediator always decays into a b-quark-DM pair. Of the three parameters of the model, the mediator and DM masses and the coupling, λb , only the first two are varied, while the last one is set to the value predicting a DM relic density compatible with astro- physical observations [136]. Representative diagrams for these models are presented in figures 4b and 4c. 3. In the SCCt model, the mediator, ηt , consists of a SU(2)L -singlet field that couples to right-handed quarks, and is produced by down-type quark-anti-quark fusion, and it decays into a top quark and a DM particle. The representative diagram is shown in figure 4d. This specific realisation of the model [109], which gives rise to a char- acteristic signature composed of a single top quark and an invisible particle, can be related to the MSSM if an additional R-parity violating interaction of the top squark with the down-type quarks is assumed. The coupling strength of the mediator to DM and top quarks, denoted by λt , and the coupling strength to light-flavour down-type quarks, gds , are free parameters of the model. 2.3 Extended Higgs sector dark matter models The third category of models aims to extend the simplified DM mediator models by involv- ing an extended two-Higgs-doublet sector (2HDM) [148–156], together with an additional mediator to DM, either a vector or a pseudo-scalar. This embeds the simplified models in a UV-complete and renormalisable framework and allows the investigation of a broad phenomenology predicted by these types of models. In both models, the 2HDM sector has a CP-conserving potential and a softly broken Z2 symmetry [157], and the alignment limit is assumed, so that the lightest CP-even state, h, of the Higgs sector can be identified with the SM Higgs boson. –8– q̄ f q̄ h ZV0 χ ZV0 A q f¯ q χ̄ (a) (b) Figure 5. Schematic representation of the dominant production and decay modes for the JHEP05(2019)142 0 2HDM+ZV model. 2.3.1 Two-Higgs-doublet models with a vector mediator The first two-Higgs-doublet model [158], denoted for brevity 2HDM+ZV 0 in the following, is based on a type-II 2HDM [157, 159] with an additional U(1) gauge symmetry, which gives rise to a new massive ZV 0 gauge boson state. The Z 0 boson, which can mix with V the Z boson, couples only to right-handed quarks and only to the Higgs doublet that couples to the up-type fermions. The CP-odd scalar mass eigenstate, A, from the extended Higgs sector couples to DM particles and complies with electroweak precision measurement constraints. The phenomenology of this model is extended with respect to the simplified case due to the presence of a new decay mode ZV 0 → hA, as shown in figure 5, with the A boson decaying into a pair of DM particles with a large branching ratio (when kinematically possible), as long as the decay into a pair of top quarks is kinematically forbidden [32]. Additional signatures involving decays of the ZV 0 boson into SM particles or the H and H ± bosons are possible in the model. However, the model parameters are chosen in order to be consistent with the constraints from searches for heavy-boson resonances on this model [160], and therefore these signatures are not considered further in the context of this interpretation. The model has six parameters [160]: tan β, the ratio of the vacuum expectation values of the two Higgs doublets, is set to unity; mχ , the DM mass, is set to 100 GeV; and gZ , the coupling of the new ZV 0 U(1) gauge symmetry, is set to 0.8. The masses mh and mH = mH ± of the two CP-even and charged Higgs bosons are set to 125 GeV, and 300 GeV, respectively, while mA , the mass of the CP-odd Higgs partner and mZV0 are free parameters and varied in the interpretation. 2.3.2 Two-Higgs-doublet models with a pseudo-scalar mediator The second 2HDM model [152], 2HDM+a, includes an additional pseudo-scalar mediator, a. In this case also, the 2HDM coupling structure is chosen to be of type-II, although many of the interpretations in this paper hold for a type-I case too. The additional pseudo-scalar mediator of the model couples the DM particles to the SM and mixes with the pseudo- scalar partner of the SM Higgs boson. The physics of the model is fully captured by 14 parameters: the masses of the CP-even (h and H), CP-odd (a and A) and charged (H ± ) bosons; the mass of the DM particle (mχ ); the three quartic couplings between the scalar –9– doublets and the a boson (λP1 , λP2 and λ3 ); and the coupling between the a boson and the DM, yχ ; the electroweak VEV, v; the ratio of the VEVs of the two Higgs doublets, tan β; and the mixing angles of the CP-even and CP-odd weak eigenstates, α and θ, respectively. The coupling yχ = 1 is chosen, having a negligible effect on the kinematics in the final states of interest. The alignment and decoupling limit (cos(β − α) = 0) is assumed, thus h is the SM Higgs boson and v = 246 GeV. The quartic coupling λ3 = 3 is chosen to ensure the stability of the Higgs potential for our choice of the masses of the heavy Higgs bosons which are themselves fixed to the same value (mA = mH ± = mH ) to simplify the phenomenology and evade the constraints from electroweak precision measurements [152]. The other quartic couplings are also set to 3 in order to maximise the trilinear couplings JHEP05(2019)142 between the CP-odd and the CP-even neutral states. This model is characterised by a rich phenomenology. The production of the lightest pseudo-scalar is dominated by loop-induced gluon fusion, followed by associated production with heavy-flavour quarks or associated production with a Higgs or Z boson (figures 6a–6c). Furthermore, according to the Higgs sector’s mass hierarchy, Higgs and Z bosons can be produced in the resonant decay of the heavier bosons into the lightest pseudo-scalar (see for example figures 6d–6f). The pseudo-scalar mediator can subsequently decay into either a pair of DM particles or a pair of SM particles (mostly top quarks if kinematically allowed), giving rise to very diverse signatures. The four-top-quark signature [161] is particularly interesting in this model if the neutral Higgs partner masses are kept above the tt̄ decay threshold, since, when kinematically allowed, all heavy neutral bosons can contribute to this final state, as depicted in the diagram of figure 6c. Four benchmark scenarios [78] that are consistent with bounds from electroweak precision, flavour and Higgs observables are chosen to investigate the sensitivity to this model as a function of relevant parameters: ma , mA , tan β, sin θ and mχ . 2.4 EFT model of scalar dark energy The Horndeski theories [94] introduce a dark energy scalar which couples to gravity and provide a useful framework for constraining the cosmological constant problem and the source of the acceleration of the expansion of the universe. The model considered in this paper is an EFT implementation of these theories [82]. In this model, the dark energy field is assumed to couple to matter universally. The model contains two classes of effec- tive operators: operators which are invariant under shift-symmetry φDE → φDE + constant, where φDE denotes the DE scalar field, and operators which break this symmetry. Shift- symmetric operators contain derivative interactions of φDE with the SM particles, while operators that break the shift-symmetry contain direct interactions of φDE with the SM. In the former case the DE scalar is pair-produced and does not decay within the volume miss in the detector, while the latter case in- of collider experiments, thereby resulting in ET cludes Yukawa-type interactions φDE ψ̄ψ, which allow the scalar to decay into SM fermions, thereby changing the expected signatures. The interactions arising from the shift-symmetry breaking operators are tightly constrained [162] and are not evaluated here. There are nine shift-symmetric Lagrangian effective operators in the model, each sup- pressed by powers of a characteristic energy scale M according to the operator’s dimen- – 10 – g g g g b/t t χ t b/t b/t/(χ) A/a A/H/a t t H/A/a t̄ χ̄ t̄ b̄/t̄ b̄/t̄/(χ̄) g g g b̄/t̄ (a) (b) (c) g b t JHEP05(2019)142 g Z/h Z/γ/g/h χ t t A/H t χ t t H− t̄ a a χ̄ χ t̄ A/a g χ̄ g χ̄ g W− (d) (e) (f ) Figure 6. Schematic representation of the dominant production and decay modes for the 2HDM+a model. g g g t φ DE g g φ φ DE DE g t̄ g φ DE (a) (b) Figure 7. Schematic representation of representative production modes for the DE model for the Lagrangian effective operators (a) L1 and (b) L2 . sionality: 9 9 X X ci (d) L = LSM + ci Li = LSM + Oi , i=1 i=1 Mid−4 where d is the operator’s dimension and ci are the Wilson coefficients. Operators L1 –L5 correspond to interactions of the DE field with SM fields. The leading, i.e. least suppressed, operators of dimension eight are ∂µ φDE ∂ µ φDE ν L1 = Tν M14 ∂µ φDE ∂ν φDE µν L2 = T , M24 – 11 – where T µν is the energy-momentum tensor corresponding to the SM Lagrangian. The L1 operator corresponds to a derivative coupling of the DE field to the conformal anomaly, Tνν (= mψ̄ψ for a Dirac field), and is therefore proportional to the mass of the SM fermions to which DE couples. Signatures which probe DE production in association with tt̄ are therefore the most sensitive to this type of coupling and are used here. The L2 opera- tor involves derivatives of the SM fields and is therefore proportional to their momenta. Final states involving large momentum transfers, such as the jet+ET miss signature, offer the highest sensitivity to this type of coupling. The L1 and L2 operators are referred to as (kinetically dependent) conformal [163] and disformal, respectively. Operators L3 –L5 correspond to higher-order versions of L1 and L2 . The operator L6 corresponds to a gen- JHEP05(2019)142 eralised kinetic term for the DE scalar and operators L7 –L9 correspond to the non-trivial Galilean terms [164]. In this paper, only L1 and L2 are considered. Due to the absence of terms allowing the decay of the DE scalars into SM particles, the DE particles (φDE ) are stable and they escape the detector producing a missing-momentum signature. The validity of the EFT approach in the context of collider data [165–167] is assessed √ √ with the procedure described in ref. [75], imposing the condition ŝ < g∗ M , where ŝ is the centre-of-mass energy of the hard interaction and g∗ is the effective coupling associated with the UV completion of the EFT. Representative Feynman diagrams corresponding to the L1 and L2 operators for the miss and mono-jet signatures are shown in figure 7. tt̄ + ET 3 Dataset and signal simulation This paper interprets analyses of pp collision data recorded at a centre-of-mass energy of √ s = 13 TeV by the ATLAS detector during 2015 and 2016. Unless otherwise specified, the integrated luminosity of the dataset, after requiring that all detector subsystems were operational during data recording, amounts to 36.1 ± 0.8 fb−1 . Monte Carlo (MC) simulated event samples were used to aid in the estimation of the background from SM processes and to model the DM and DE signals. Simulated events were processed either through a detector simulation [168] based on Geant4 [169] or through a fast simulation [168] with a parameterisation of the calorimeter response and Geant4 for the other parts of the detector [170]. Either of these ATLAS detector simulations were used for background processes (details in the specific analysis references) and most of the signal processes, as detailed in the following. Two sets of samples were used for the modelling of the signal processes considered in this paper. One set of samples is based on signal events processed through the ATLAS detector simulation, referred to as “reconstructed” samples. The second set of samples consists of signal events composed of particle-level objects, defined according to the guiding principles outlined in ref. [171], and not including any resolution effect due to the ATLAS detector. These are referred to as “particle-level” samples. Particle-level samples were used to define a rescaling procedure specifically designed to broaden the range of signal models and parameter choices considered in the interpretation of the results. The procedure allows the use of less extensive computational resources that would be needed to provide a – 12 – full detector simulation for the large set of considered signals, while providing a complete picture of the current experimental coverage for these models. The rescaling procedure calculated a set of correction weights for a reference model as the ratio of the acceptance for a baseline signal sample to the acceptance of the signal sample of interest. Both of these acceptances are derived in a particle-level simulation. These weights were then applied to the reconstructed baseline signal sample of the reference model, assuming similar detector effects for the two models. The same procedure was used in some cases to rescale between signal samples of the same reference model but for different parameter choices which affect the kinematics of the final state. Closure-tests were performed to determine the reliability of this procedure and assign specific systematic uncertainties when needed. Further details JHEP05(2019)142 about the rescaling used in the V/AV, VFC and the 2HDM+a signal samples are given in appendix A. The generation settings for signal models considering a spin-1 mediator are summarised in table 4. For each model the table indicates the Universal FeynRules Output (UFO) model [172] implementation, the matrix element (ME) generator, the parton shower (PS), and the cross-section normalisation, at QCD leading-order or next-to-leading order ac- curacy (LO and NLO, respectively). Following the notation of the previous section, the simplified models are indicated with ZV/A0 , while the baryon-charged and flavour-changing 0 interactions are indicated as ZB and ZVFC 0 , respectively. The 2HDM model with an ad- ditional vector mediator is indicated as 2HDM+ZV 0 . When relevant for the generations settings, each separate final state considered in this paper is indicated for each model. The generation settings for signal models considering a spin-0 mediator are summarised in table 5. Following the notation of the previous section, the colour-neutral (colour- charged) simplified models are indicated with φ/a (η). The 2HDM with additional pseudo- scalar mediator is indicated as 2HDM+a. The model implementations, settings and parameter scans follow the prescriptions of the DM Forum/LHC DM Working Group [75–78]. Finally, the generation settings for the DE model are also indicated in table 6. 4 Experimental signatures Dark matter searches are an important component of the ATLAS physics programme. Several final-state signatures are targeted to maximise the discovery potential. This section presents summaries of the different searches for DM and is not intended to be exhaustive. More details are available in the reference papers. Table 2 summarises the DM searches for invisible final states, while table 3 summarises the searches for visible final states. These tables also provide an overview of the models (table 1) which are constrained by each of these signatures and which of these intepretations have not been presented elsewhere. Electrons, muons, photons and jets are reconstructed by combining the signals from the different components of the ATLAS detector3 [173–177]. Leptons (`) in the following 3 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the z-axis along the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upwards. Cylindrical coordinates (r, φ) are used in the transverse – 13 – refers to electrons or muons. In several analyses, events with identified leptons are rejected from the signal region selection. This is referred to as a lepton veto. The analyses may implement different lepton and photon selection criteria for particle identification [173, 175, 176, 178], isolation [173, 175, 179], and kinematic requirements (pT , η). Small-R and large-R jets are reconstructed from energy deposits in the calorimeters using the anti-kt jet algorithm [180, 181] and using a radius parameter of R = 0.4 and R = 1.0, respectively. Reclustered large-R jets are reconstructed from small-R jets using a radius parameter of either R = 0.8 or R = 1.2. Multivariate algorithms are used to identify small-R jets with pT > 20 GeV containing b-hadrons (b-jets) [182, 183]. This is referred to as b-tagging. For large-R jets, b-tagging is applied to their associated track-jets, which are constructed from JHEP05(2019)142 tracks reconstructed in the inner detector using the anti-kt jet algorithm with R = 0.2. The missing transverse momentum p~Tmiss (with magnitude ET miss ) is calculated from the negative vector sum of transverse momenta (pT ) of electrons, muons and jet candidates and an additional soft term [184] which includes activity in the tracking system originating from the primary vertex but not associated with any reconstructed particle. Some analyses may also consider photons in the ET miss reconstructions. 4.1 Searches for invisible final states Searches for WIMP candidates at the LHC are characterised by the requirement of large ETmiss since WIMPs escape detection. Therefore, final states with additional visible particles are considered in the selection of the events. These additional particles may come from initial-state radiation or from associated production. Several signatures that are listed in the following are exploited and optimised to enhance the sensitivity to different DM models. Jet +ET miss . The jet+E miss analysis [26], commonly referred to as the mono-jet analysis, T is characterised by the presence of an energetic jet and large ET miss . The analysis selects events with ET miss > 250 GeV, at least one jet with p > 250 GeV, and at most three T additional jets with pT > 30 GeV. Events are required to pass a lepton veto. To reduce the contribution from multi-jet background where large ET miss can originate from jet energy under-measurement, a minimum separation in the azimuthal angle between each selected jet and the ET miss direction is also required: ∆φ(jet, p ~Tmiss ) > 0.4. The W +jets, Z+jets, and top-quark-related backgrounds are constrained using MC event samples normalised to data in selected control regions containing leptons. In the case of W +jets and Z+jets events, MC predictions are reweighted to account for higher-order QCD and electroweak corrections as a function of the vector-boson pT [185]. The normalisation factors for these backgrounds are extracted simultaneously using a binned likelihood fit of the ET miss distributions in all control and signal regions that includes systematic uncertainties. The remaining SM backgrounds from diboson processes are determined using MC simulated samples, while the multi-jet background contribution is extracted from data. plane, φ being the azimuthal angle around the z-axis. The pseudorapidity is pdefined in terms of the polar angle θ as η = − ln tan(θ/2). Angular distance is measured in units of ∆R ≡ (∆η)2 + (∆φ)2 . The rapidity is defined at y = 1/2 ln[(E + pz )/(E − pz )], where E is the energy and pz is the component of its momentum along the z-axis. The rapidity difference between two jets is defined as y ∗ = (y1 − y2 )/2. – 14 – h(inv). Searches for invisible Higgs boson decays have been performed using several √ production and decay channels at a centre-of-mass energy of s = 8 TeV [29]. Results of searches in the vector-boson fusion (VBF) production channel and in associated production of a Higgs boson with a W/Z boson are statistically combined with the measured production and decay rates of the Higgs boson in the γγ, ZZ, W W , Zγ, bb, τ τ , and µµ channels to set an upper limit on the Higgs boson’s invisible branching ratio of 0.23 at 95% confidence level (CL). This combined limit is used in the results quoted in section 6. Among the direct searches, the VBF production of Higgs bosons decaying into invisible particles [186] is the most sensitive one, setting an upper limit on the invisible branching ratio of 0.28. The VBF+ET miss analysis requires E miss > 150 GeV and two jets with p > 35 GeV. Three JHEP05(2019)142 T T orthogonal signal regions are defined by varying the threshold imposed on the leading jet pT and the invariant mass of the two jets. Additional requirements on the angular separation of the two jets are applied to enhance the sensitivity to VBF production. In particular, the two leading jets are required to be well separated in pseudorapidity. Lepton and b- jet vetoes are applied to reduce contamination from W +jets and top-quark backgrounds, respectively. Dedicated control regions with one and two leptons in the final state are used to constrain the contributions from dominant Z/W +jets backgrounds, through a simultaneous fit together with the signal region. The multi-jet background is estimated using a data-driven technique. Searches for Zh(inv) and V h(inv) [20, 24, 187] have been √ miss analysis performed at centre-of-mass energy s = 13 TeV. Constraints using a VBF+ET √ are also available using s = 13 TeV pp collision data [188, 189]. However, the 8 TeV combination gives more stringent limits, thus it is used here. γ + ET miss . Events in the γ + E miss analysis [21] are required to pass the lepton veto and T to have a photon with ET > 150 GeV. Events with more than one jet (pT > 30 GeV) or with a jet fulfilling ∆φ(jet, p~Tmiss ) < 0.4 are rejected. Three exclusive signal regions with ET miss ranges between 150 GeV, 225 GeV, 300 GeV and above are defined. The W γ, Zγ, and γ+jets backgrounds are normalised in control regions using a simultaneous likelihood fit of all ET miss regions, but with independent normalisation factors for each region. The backgrounds due to photons from the misidentification of electrons or jets in processes such as W/Z+jets, diboson, and multi-jet events are estimated using data-driven techniques. Z(``) + ET miss . The event selection criteria in this analysis [24] require large E miss and T a pair of high-pT leptons. Two opposite-sign, same-flavour leptons satisfying pT > 30 GeV and pT > 20 GeV are required. The lepton pair is required to have an invariant mass between 76 GeV and 106 GeV to be consistent with originating from a Z boson. Events with an additional lepton with pT > 7 GeV or a b-jet with pT > 20 GeV are vetoed. To target events consistent with a boosted Z boson produced in the direction opposite to p~Tmiss , additional requirements are imposed on the azimuthal angle between the dilepton system and p~Tmiss and on the angular distance between leptons. A single inclusive ET miss signal region is defined with ETmiss > 90 GeV for each of the ee and µµ channels. The dominant background in this analysis, ZZ production, is estimated from MC simulation. The W Z background is normalised to data in a three-lepton control region. The contributions from Z+jets and non-resonant-`` backgrounds are estimated using data-driven techniques. A statistical combination of the two decay channels is used for the final results. – 15 – W (qq 0 )/Z(q q̄) + ET miss . This analysis [20] selects events with E miss > 150 GeV and T a hadronically decaying W or Z boson candidate. The vector-boson candidate is defined with one large-R jet with pT > 250 GeV in a boosted topology (ET miss > 250 GeV) or with two small-R jets with pT > 20 GeV in a resolved topology. In both cases, a lepton veto is applied. Additional requirements are applied to the invariant mass of the boson candidate. Several signal regions are defined according to the b-jet multiplicity. Similarly, several control regions are defined according to lepton and b-jet multiplicity. The normali- sations of the tt̄ and W/Z+jets background processes are constrained using a simultaneous miss distribution. The subdominant contribu- fit of all control and signal regions of the ET tion from diboson and single-top-quark production is obtained from simulation. Multi-jet JHEP05(2019)142 contributions are estimated with a data-driven technique. h(bb̄) + ET miss . The h(bb̄) + E miss analysis [23] is defined by the requirement of E miss > T T 150 GeV, a lepton veto, and the presence of a Higgs boson candidate decaying to two b-jets with suitable invariant mass. Events with mis-measured ET miss are rejected by imposing constraints on ∆φ(jet, p~Tmiss ), between the missing momentum direction and the direction of any selected jet in the event. Two sets of signal regions are defined targeting moderate- momentum (resolved) and high-momentum (boosted) Higgs boson candidates. In each case, the regions are further split according to whether there are one or two b-jets. The resolved regime, defined in three exclusive ET miss regions between 150 GeV and 500 GeV, selects a Higgs boson candidate reconstructed from the two leading b-tagged small-R jets (or from a b-tagged and a non-b-tagged small-R jet) with pT > 20 GeV. In the boosted regime, defined by ET miss > 500 GeV, the leading large-R jet with p > 200 GeV is the Higgs boson T candidate. The b-jet multiplicity is defined by the number of b-tagged track-jets associated with the large-R jet. Backgrounds involving the production of W/Z bosons in association with heavy-flavour quarks or top-quark pairs are normalised in dedicated control regions distinct from the signal regions by requiring one or two leptons. A simultaneous binned likelihood fit to the invariant mass of the Higgs boson candidate is performed in all signal and control regions. The multi-jet background is obtained with a data-driven technique. Other subdominant backgrounds are estimated from simulation. h(γγ) + ET miss . The h(γγ) + E miss events in this analysis [22] are selected by requiring at T least two photons with pT > 25 GeV. The two leading photons are chosen to reconstruct the Higgs candidate, which is required to satisfy 105 GeV < mγγ < 160 GeV. The leading γ (sub-leading) photon is also required to have ET /mγγ > 0.35 (0.25). Events with leptons ET > 7 GeV1/2 in ref. [22] are miss / pP are vetoed. Events with pT (γγ) > 90 GeV and ET P used for the interpretation of DM models, where ET is the scalar sum of the transverse momentum of all reconstructed objects in the event. The backgrounds are extracted by fitting an analytic function to the diphoton invariant mass distribution. In the case of the non-resonant background, the normalisation and shape are obtained by fitting the invariant mass distribution in data to an exponential function. The SM Higgs boson background shape is modelled with a double-sided Crystal Ball function and fitted to the MC simulation. – 16 – t+ET miss . The t+E miss analysis [30] searches for events with one top quark and relatively T large ETmiss . Two signal regions are defined depending on the decay channel of the top quark. The leptonic channel selects events with a positively charged lepton with pT > 30 GeV, ETmiss > 50 GeV, and transverse mass of the lepton and the E miss , mW , larger than 260 GeV. T T One b-jet with pT > 30 GeV is additionally required. The hadronic channel is optimised to select events with a top quark produced with a large boost. Events are selected with ET miss > 200 GeV and one large-R jet with pT > 250 GeV with one b-tagged track-jet associated with it. Events failing the lepton veto are rejected. Dedicated control regions are defined to constrain the tt̄ and W/Z+jets backgrounds from data. The multi-jet background is estimated from data, whereas other remaining backgrounds are taken from simulation. All JHEP05(2019)142 signal and control regions for the two decay channels are fitted simultaneously to extract the background normalisation. In the case of the hadronic channel, the transverse mass of the large-R jet and the ET miss are the discriminating variables, while for the leptonic channel, the ET miss distribution is used to discriminate signal from background. b(b̄) + ET miss . The b + E miss analysis [25] selects events with two energetic jets (p > T T 160 GeV), at least one of which is b-tagged, ET miss > 650 GeV, and additional total hadronic energy restricted to be less than 100 GeV. This last requirement rejects top-quark back- ground. The dominant background for this analysis, Z+jets events, is constrained from data in a dedicated control region, which is fitted together with the signal region. The bb̄ +ETmiss analysis [25] instead exploits a selection with at least two b-jets and a consid- erably lower ET miss requirement, E miss > 180 GeV. The azimuthal separations between T the b-jets and p~Tmiss are exploited to enhance the separation between the signal and the irreducible background in this channel (Z(ν ν̄)+bb̄), which is constrained from data in a dedicated control region. The results are extracted by fitting an observable that relies on the pseudorapidity difference between the two b-jets: cos θbb∗ = |tanh (∆η /2)|. bb miss . The tt̄ +E miss analysis [25, 27, 28] is split into three channels according to the tt̄ + ET T decays of the W bosons from the top-quark decays: 0-lepton, where both W bosons decay hadronically, 1-lepton, where one of the two W bosons decays leptonically and 2-leptons where both W bosons decay leptonically. The analyses targeting the 0-lepton channel exploit two sets of signal topologies: spin-0 DM models [25], used for the DM interpretations presented in this paper, and top-squark decays into a top quark and a neutralino [28], used for the DE interpretation in this paper. Both analyses are characterised by a set of signal regions which select events with at least four energetic jets, at least two of which are b-tagged, and relatively high ET miss . Requirements on the invariant mass of reclustered large-R jets are imposed to identify events where a W boson or a top quark are boosted. The dominant backgrounds (Z+jets, top-quark processes and tt̄ + Z) are constrained in dedicated control regions. The three signal regions used for the DE interpretation are statistically combined, while the two signal regions in the DM analysis are not. The analysis targeting the 1-lepton channel selects events with at least four energetic jets, at least one of which is b-tagged, one isolated lepton and high ET miss . The events are also required to have at least one hadronic top candidate with invariant mass loosely compatible with the mass of the top quark. Requirements on the transverse and asymmetric stransverse masses [27] – 17 – Analysis Models targeted Final-state signature Key Characteristics Results miss V/AV(∗), S/PS(∗), miss miss Section 6.1.1, 6.2.1, Jet +ET [26] 1–4 jets, ET , 0 `. Binned likelihood fit of ET . SCCq (∗), DE 6.2.2, 6.4 miss Section 6.3.2 h(inv)[29, 186] 2HDM+a 2 jets, ET , mjj , ∆ηjj . Single-bin likelihood fit. miss miss miss γ+ ET [21] V/AV(∗) 1 photon, 0–1 jets, ET , 0 `. Binned likelihood fit of ET . Section 6.1.1 miss miss miss Z(``) + ET [24] V/AV, 2HDM+a 2 `, ET , m`` ∼ mZ . Binned likelihood fit of ET Section 6.1.1, 6.3.2 miss ET , W/Z candidate (resolved and W/Z(qq 0 ) + ET miss [20] V/AV, 2HDM+a miss Binned likelihood fit of ET . Section 6.1.1, 6.3.2 boosted topologies). VBC, miss miss 0 ET , h candidate (resolved and Binned likelihood fit of mh in bins Section 6.1.2, 6.3.1, h(bb̄) + ET [23] 2HDM+ZV (∗), miss boosted topologies). of ET . 6.3.2 2HDM+a VBC, miss 0 miss Section 6.1.2, 6.3.1, h(γγ) + ET [22] 2HDM+ZV (∗), 2 photons, mγγ ∼ mh , ET . Analytic function fit of mγγ . 6.3.2 JHEP05(2019)142 2HDM+a miss Binned likelihood fit of ET miss miss miss t + ET [30] VFC ET , t candidate (all decay channels). (mT (ET , large-R jet)) in the lep- Section 6.1.3 tonic (hadronic) channel. miss S/PS(∗), SCCb (∗), miss ∗ Section 6.2.1, 6.2.2, b(b̄) + ET [25] 1–2 b-jets, ET , 0 `. Binned likelihood fit of cos θbb . 2HDM+a 6.3.2 miss S/PS(∗), SCCt (∗), miss Section 6.2.1, 6.2.2, tt̄ + ET [25, 25, 27] 0–2`, 1–2 b-jets, ≥1–4 jets, ET , m`` T2 . Binned likelihood fit. 2HDM+a, DE 6.3.2, 6.4 Table 2. Summary of searches for invisible final states used to constrain the different DM models defined in section 2. The (∗) indicates models which were presented in the original publication, all others are either new or updated. are used to suppress semileptonic and dileptonic tt̄ events, respectively. Requirements on the azimuthal angle between the lepton and p~Tmiss and on ∆φ(jets, p~Tmiss ) are also exploited to further suppress the background contamination of the signal regions. All top-quark background processes are estimated in dedicated control regions. Finally, the analysis targeting the 2-lepton channel selects events with two opposite-sign leptons which are inconsistent with being produced in the decay of a Z boson. At least one b-jet is also required in the selections. The ET miss and the stransverse mass (m`` [25]) requirements are T2 such that m`` T2 + 0.2 · E miss > 170 GeV. The dominant backgrounds in this channel (tt̄ and T tt̄ + Z) are estimated in dedicated control regions. None of these analyses shows a significant deviation from the expected SM background, and thus exclusion limits can be set for the relevant models. These limits are discussed in section 6. The observed ET miss distributions compared with the background predictions are shown in figure 8 for the h(bb̄) + ET miss and Z(``) + E miss analyses, with representative T 2HDM+a signal distributions shown in each case. These two analyses have the strongest 2 sensitivity for this model, as discussed in section 6.3.2. The observed mχT2 and ET miss distributions compared with the background predictions are shown in figure 9 for the tt̄ +ET miss (0-lepton channel) and jet+E miss analyses, respectively, with representative DE T signal distributions shown in each case. Figures 8 and 9 show background predictions after the corresponding fit in each analysis. 4.2 Searches for visible final states Several searches for narrow resonances are interpreted in terms of the DM models described in section 2. These searches explore several final-state signatures by selecting different – 18 – 109 107 Events / bin Events / bin Data Data ATLAS ATLAS Z+jets 108 Z+jets s = 13 TeV , 36.1 fb miss -1 t t + single top 106 s = 13 TeV , 36.1 fb miss -1 t t + single top H(bb) + ET W+jets H(bb) + ET W+jets 107 0 lepton 1 b-tag Diboson 0 lepton 2 b-tags Diboson SM Vh 105 SM Vh 106 Multijet Multijet Background Uncertainty Background Uncertainty 105 Pre-fit Background 104 Pre-fit Background 2HDM+a 2HDM+a mH=1 TeV, ma =250GeV mH=1 TeV, ma =250GeV 104 σSignal = 8.61 fb 103 σSignal = 8.61 fb 3 10 2 10 102 10 JHEP05(2019)142 10 1 0 1 0 1.2 Data/SM Data/SM 1.05 1 1 0.95 0.8 200 300 400 500 600 700 800 200 300 400 500 600 700 800 Emiss T [GeV] Emiss T [GeV] (a) (b) [Events/GeV] [Events/GeV] 103 ATLAS Data Non-resonant ll 103 ATLAS Data Non-resonant ll s = 13 TeV, 36.1 fb-1 ZZ Z+jets s = 13 TeV, 36.1 fb-1 ZZ Z+jets 102 miss WZ Others 102 miss WZ Others Z(ee)+E Z(µµ)+E T Stat.+Syst. T Stat.+Syst. 10 10 dN/dEmiss dN/dEmiss 2HDM+a (m =600 GeV, ma=250 GeV) 2HDM+a (m =600 GeV, ma=250 GeV) H H T T AV (m =500 GeV, mχ=100 GeV) AV (m =500 GeV, mχ=100 GeV) ZA ZA 1 1 10−1 10−1 10−2 10−2 10−3 10−3 1.6 1.6 Data/SM Data/SM 1.4 1.4 1.2 1.2 1 1 0.8 0.8 0.6 0.6 100 200 300 400 500 1000 100 200 300 400 500 1000 Emiss T [GeV] Emiss T [GeV] (c) (d) miss miss Figure 8. Observed ET distribution in the h(bb̄)+ET analysis in the (a) 1-b-tag and (b) 2-b-tag signal regions compared with the background predictions. The error bands show the total statistical miss and systematic uncertainties of the background predictions. The expected ET distribution for a representative signal model is also shown. It corresponds to a 2HDM+a signal with ma = 250 GeV, mH = mH ± = mA = 1000 GeV, tan β = 1.0, sin θ = 0.35, gχ = 1.0 and mχ = 10 GeV. Observed miss miss ET distribution in the Z(``) + ET analysis in the (c) ee and (d) µµ signal regions compared miss with the background predictions. The expected ET distribution for representative signal models are also shown. They correspond to a 2HDM+a signal with ma = 250 GeV, mH = mH ± = mA = 600 GeV, tan β = 1.0, sin θ = 0.35, gχ = 1.0 and mχ = 10 GeV, and an AV signal with mZA0 = 500 GeV, mχ = 100 GeV, gq = 0.25, g` = 0, and gχ = 1.0. The background predictions are after the corresponding fit in each analysis. – 19 – 107 [Events/GeV] 15 Events / 50 GeV ATLAS Data 6 ATLAS Data 10 Standard Model SM Total s = 13 TeV, 36.1 fb-1 s=13 TeV, 36.1 fb-1 Z 5 jet+E miss Z(→ ν ν ) + jets 10 tt+Emiss T T , 0-lepton, ≥ 2 b-tags tt W(→ lν ) + jets dN/dEmiss Single Top 104 Z(→ ll) + jets T 10 t t +V 10 3 t t + single top W Dibosons DE, L1 M = 309 GeV 102 multijets + ncb DE, L 2 M = 1260 GeV 10 5 1 10−1 1.2 300 400 500 600 700 800 900 1000 1100 1200 Data / SM Stat. + Syst. Uncertainties 1 0 JHEP05(2019)142 600 800 2 1000 0.8 χ 300 400 500 600 700 800 900 1000 1100 1200 mT2 [GeV] miss ET [GeV] (a) (b) 2 Figure 9. Observed mχT2 and ET miss distributions in the (a) tt̄(0L) + ETmiss and (b) jet+ET miss analyses, respectively, compared with a representative DE signal and the post-fit background pre- dictions. The error bands show the total statistical and systematic uncertainties of the background predictions. Representative DE signal distributions are shown for L1 and L2 operators in (a) and (b), respectively. visible particles, thus requiring the presence of reconstructed objects such as jets or leptons, covering a variety of kinematic regions. In some of the analyses described below, further identification techniques are employed to select final states with top quarks. Dijet. For this analysis [190] events with at least two small-R jets are selected if the pT of the leading (sub-leading) jet is greater than 440 (60) GeV. The dijet selection requires a ra- pidity difference |y ∗ | < 0.6 and the invariant mass of the dijet system to be mjj > 1.1 TeV. The background estimation is obtained by fitting the falling mjj distribution. Bin widths are chosen to approximate the mjj resolution, and thus are wider for higher masses. A sliding-window fitting technique is used, where restricted regions of the spectrum are fitted with a functional form. The background is constructed bin-by-bin by performing a likeli- hood fit to the data in each window and using the fit value in the central bin for the back- ground estimate. The values from the full set of windows are then combined to create the background estimate for the full mass range. Model-independent limits on the visible cross- section for a hypothetical signal that produces a Gaussian contribution to the mjj distribu- tion (for several signal widths) are provided for this analysis (see appendix A of ref. [191]). This analysis was performed in data corresponding to an integrated luminosity of 37.0 fb−1 . Dijet angular. A dijet selection can also be exploited to search for deviations from the SM expectation in angular distributions, characteristic of wider resonances where the nominal dijet search would lose sensitivity. A dijet angular analysis [190] is performed in events with two jets following the pT requirements of the dijet search, but relaxing the |y ∗ | requirement to 1.7. Due to different kinematics in this loosened selection, the mass of the dijet pair is required to be mjj > 2.5 TeV. The analysis makes use of the variable – 20 – ∗ χjj = e2|y | ∼ (1 + cos θ∗ )/(1 − cos θ∗ ),4 constructed so that, in the limit of massless parton scattering and when only the t-channel scattering contributes to the partonic cross-section, the angular distribution dN/dχjj is approximately independent of χjj . MC events from multi-jet production are modelled at LO in QCD, and reweighted to NLO predictions from NLOJET++ [192, 193] using mass- and angle-dependent correction factors. Addi- tional electroweak mass- and angle-dependent correction factors are applied. The data are compared with a SM template in different mjj ranges, and different χjj bins. Trigger-object-level dijet. For the dijet analysis described before, the high pT thresh- old imposed on the leading jet is limited by the trigger selection driven by the bandwidth JHEP05(2019)142 available for single-jet triggers, thus it only targets mjj > 1.5 TeV. The limitation from the high-level trigger selection is overcome by recording only high-level trigger jet information, rather than the full detector readout, to a dedicated data stream, reducing the storage needs per event. This strategy allows to record all events passing the single-jet level-one (L1) trigger (with lower threshold than in the high-level trigger) with minimal bandwidth increase. The dataset collected corresponds to an integrated luminosity of 29.3 fb−1 . This trigger-object-level dijet analysis (TLA dijet) [194] selects events with at least two trigger- level jets with pT > 85 GeV. Two selection criteria are used: |y ∗ | < 0.6 in the mass range 700 GeV < mjj < 1.8 TeV and |y ∗ | < 0.3 for 450 GeV < mjj < 700 GeV. The leading trigger-level jet is required to have pT > 185 GeV and pT > 220 GeV for the |y ∗ | < 0.3 and |y ∗ | < 0.6 selections, respectively, to ensure full efficiency for the L1 triggers. The search is then interpreted in terms of resonances with a mass between 450 GeV and 1.8 TeV. The background strategy used in the dijet search is also used here. Resolved dijet + ISR. Another alternative strategy to search for low-mass dijet res- onances is to select events with a pair of jets recoiling against a photon or an additional jet from ISR. The resolved dijet + ISR analyses [195] select events with a high-pT ISR object (γ or jet), used to trigger the event, and a relatively low mass dijet resonance. Dijet+γ events contain at least one photon with pγ > 150 GeV and at least two jets with pT > 25 GeV. The two leading jets must satisfy |y ∗ | < 0.8, which allows to probe of dijet invariant masses between 170 GeV and 1.5 TeV. The three-jet selection requires at least one jet with pT > 430 GeV as well as two additional jets with pT > 25 GeV. The leading jet is chosen as the ISR candidate, and the second- and third-highest-pT jets are required to satisfy |y ∗ | < 0.6. This selection probes a mass range between about 300 GeV and 600 GeV. The background contribution is estimated by fitting the mjj distribution. This analysis was performed in 13 TeV collision data corresponding to an integrated luminosity of 15.5 fb−1 . Boosted dijet + ISR. In the case of a dijet+ISR selection, if the associated ISR photon or jet has large transverse momentum, the dijet resonance candidate is reconstructed as a large-R jet [196] of radius 1.0 with mass m. To enhance the sensitivity to quark pair decays, jet substructure techniques are used to discriminate between a two-particle jet from a decay 4 ∗ θ is defined as the polar angle with respect to the direction of the initial partons in the dijet centre- of-mass frame. – 21 – of a boosted resonance and a single-particle jet [197]. Events are required to have a large- R jet, the resonance candidate, and at least one ISR object candidate. The azimuthal angular separation between the resonance candidate and the ISR object is required to satisfy ∆φ > π/2. A pT > 2m requirement ensures sufficient collimation of the resonance candidate. In the ISR jet (photon) channel, the large-R jet satisfies pT > 450 (200) GeV and the ISR jet (photon) has pT > 450 (155) GeV. A data-driven technique is used to model the expected background in the signal region via a transfer factor that extrapolates from a control region with inverted jet substructure requirements. Dibjet. The dibjet search [198] targets dijet resonances with one or two jets identified as JHEP05(2019)142 b-jets. Two different analyses cover both the low and high invariant mass regions. Events in the high invariant mass region are selected with at least two jets, one of which has pT > 430 GeV and passes an inclusive jet trigger. The rapidity difference is required to be |y ∗ | < 0.8. This analysis covers the region with mjj > 1.2 TeV. The low invariant mass region uses a trigger targeting events with two jets containing b-hadrons, which provides access to lower dibjet invariant masses (mjj ) compared to the single jet trigger: 570 GeV < mjj < 1.5 TeV. The rapidity difference requirement is tightened to |y ∗ | < 0.6. In this case, only the two-b-jets selection is considered. Because the double b-jet trigger was not available during the full data-taking period, the total integrated luminosity used for the low-mass analysis corresponds to 24.3 fb−1 of 13 TeV collision data. A background estimation strategy similar to that of the dijet analysis is used in these analyses. Dilepton. The dilepton analysis [199] selects events with at least two same-flavour lep- tons. The pair of electrons (muons) with highest ET (pT ) are chosen as the candidate decay products of the resonance. Only the muon channel candidates are required to have oppo- site charge, due to higher charge misidentification for high-ET electrons and the pT mis- reconstruction associated with wrongly measured charge in muons. Background processes with two prompt leptons are modelled using MC samples. The Z/γ ∗ → `` background is smoothed for 120 GeV < m`` < 1 TeV. This is done by fitting the MC spectrum and the resulting fitted function is used to set the expected event yields in that mass range. A data-driven method is employed to estimate backgrounds with at least one misidentified lepton. The m`` distribution is explored between 80 GeV and 6 TeV. Same-sign tt. Events in the same-sign tt analysis [110] are selected with exactly two leptons with positive charge and at least one b-jet. Events are required to satisfy HT > 750 GeV, where HT is defined as the scalar sum of the pT of all selected objects, includ- ing jets. Additionally, requirements on ETmiss and the azimuthal separation between the two leptons are imposed. Signal regions for the different lepton flavours (ee, eµ and µµ) are treated separately. Irreducible SM backgrounds are determined using MC simulation samples. Backgrounds from fake leptons are estimated using data-driven techniques. tt̄ resonance. The tt̄ resonance analysis [200] selects events with two top-quark can- didates. Events are required to have a leptonic top-quark decay, selected by requiring a charged lepton and ETmiss consistent with a leptonic decay of a W boson, and a small-R jet – 22 – Analysis Models targeted Final-state signature Key Characteristics Results ∗ Sliding-window fit of the mjj distri- Dijet [190] V/AV 2 jets, mjj , y . Section 6.1.1 bution. Dijet angular [190] V/AV 2 jets, mjj , y ∗ . Binned likelihood fit of χjj . Section 6.1.1 ∗ Sliding-window fit of the mjj distri- TLA dijet [194] V/AV 2 trigger-level jets, mjj , y . Section 6.1.1 bution. Parametric function fit of the mjj Resolved dijet+ISR [195] V/AV 3 jets (or 2 jets and 1 photon), mjj , y ∗ . Section 6.1.1 distribution. Data-driven extrapolation from Boosted dijet+ISR [196] V/AV(∗) 1 large-R jet, 1 jet or photon, mJ . Section 6.1.1 control region via transfer factor. Sliding-window parametric fit of Dibjet [198] V/AV 2 jets (1 and 2 b-jets), mjj , y ∗ . Section 6.1.1 the mjj distribution. Z/γ ∗ → `` from fitted MC spec- Dilepton [199] V/AV 2 e or 2 µ. Section 6.1.1 JHEP05(2019)142 trum. miss Background with real leptons from Same-sign tt [110] VFC 2 same-sign `, 2 b-jets, HT , ET . Section 6.1.3 MC. 1 `, hadronic t candidate (resolved and tt̄ bkg from MC, binned likelihood tt̄ resonance [200] V/AV miss Section 6.1.1 boosted topologies), ET . fit of mtt̄ . Parameterised extrapolation from low to high jet multiplicity. Binned tt̄tt̄ [201] 2HDM+a 1 `, high jet multiplicity. Section 6.3.2 likelihood fit of jet and b-jet multi- plicities. Table 3. Summary of searches for visible final states used to constrain the different DM models defined in section 2. The (∗) indicates models which were presented in the original publication, all others are either new or updated. close by. Events are classified as boosted or resolved depending on their hadronic activity. In the boosted selection, events contain one large-R jet passing top-tagging requirements. In the resolved selection, events have at least four small-R jets and fail the boosted selection. The tt̄ invariant mass, mtt̄ , is reconstructed from the decay products of the two top-quark candidates in the event. The b-jet multiplicity is used for further categorisation. The SM tt̄ production is estimated using MC samples and fixed-order theory calculations. The multi-jet and W +jets background contribution is estimated using data-driven techniques. tt̄tt̄. The tt̄tt̄ analysis [201] searches for events characterised by a single lepton and high jet multiplicity. Events are categorised by their jet multiplicity, which is defined using three pT thresholds: 40 GeV, 60 GeV, and 80 GeV. Events are further separated into five bins corresponding to the b-jet multiplicity. The tt̄+jets and W/Z+jets background production is estimated using a combined fit to these jet and b-jet multiplicity bins. The normalisation of these backgrounds is extrapolated from lower to higher jet multiplicity, while the b-jet multiplicity shape is taken from a parameterised extrapolation from data (simulation) for the tt̄ (W/Z+jets) background. As in the case of the searches for invisible final states, these analyses found no signifi- cant deviation from the expected SM backgrounds. Therefore, exclusion limits are placed on the allowed phase space of the corresponding signal models, as discussed in section 6. 4.3 Complementarity and combination of signatures It can be seen from tables 2 and 3 that several analyses are often sensitive to the same model. In cases like the X +ETmiss final-states searches, X originating from initial-state radiation or – 23 – associated production, a variety of final states are evaluated: X = jet, γ, W, Z, h, t(t̄), b(b̄). Since the mediator couples DM to SM particles, it is also possible to reinterpret results from resonance searches targeting the mediator directly. The complementarity depends on the choice of model as well as coupling values. For the V/AV model, this paper considers jet/γ/V + ET miss , dijet, dibjet and tt̄ resonance final states. All results for this model are new or have been updated from previous publications, except for the jet/γ + ET miss interpretations. For the VBC and 2HDM+ZV 0 models, this paper considers only h + E miss , T which dominates the sensitivity for the chosen parameter values. All possible final states (same-sign tt and the t + ET miss ) are taken into account for the VFC model. Only invisible final states, tt̄/bb̄/jet + ET miss , are considered for the S/PS model. The SCC , SCC and JHEP05(2019)142 q b miss SCCt models are each addressed with a specific signature: jet + ET , b + ET , t + ET miss miss , respectively, and all results were presented in each specific analysis paper. Various final states are evaluated in order to place the first constraints on the 2HDM+a model by ATLAS searches: Z/h + ET miss , tt̄/bb̄+ E miss , h(inv) and tt̄tt̄. Finally, the constraints on DE models T are set using jet+ET miss and tt̄ +E miss final states. T Complementarity can also be found when studying different SM decay channels of a given signature. Two natural candidates from the analyses discussed here are the h + ET miss (bb̄, γγ) searches and the tt̄+ET miss (fully hadronic, semileptonic and fully leptonic) searches. The results from the h + ET miss searches presented in section 6.3.1 correspond to a statistical combination of the h(bb̄) + ET miss and h(γγ) + E miss searches and not published T before elsewhere. The h(bb̄)+ET miss analysis has a larger reach in mediator masses, however its sensitivity is limited at lower masses by the threshold requirement of the ET miss trigger miss used to record the events for this analysis. The h(γγ) + ET analysis covers a lower mass region owing to its selection based on a photon trigger. For the combination, the luminosity, experimental, and signal modelling uncertainties were taken to be correlated between the two channels. In the h(γγ) + ET miss analysis the systematics uncertainties are not significantly constrained by the fit. This is mainly due to the use of a single signal region and no control regions. In the case of h(bb̄) + ET miss the systematics uncertainties are constrained due to the use of dedicated control regions. It is observed, however, that the results from the combination and the individual h(bb̄)+ET miss results are very similar. While the h(bb̄) + ETmiss channel dominates the sensitivity, searches in different decay channels are of interest in probing different kinematic regions defined by different analyses strategies. For this paper, the tt̄+ET miss exclusion limits discussed in section 6 are combined based on the best expected exclusion for each signal model, unless separate contours are shown. The combination and comparison of this channel is also a novel result of this paper. 5 Systematic uncertainties Systematic uncertainties for both the background and signal models are considered in each of the analyses presented in section 4. These uncertainties, as well as statistical uncertain- ties, depend on the event selection, the phase space covered by a given analysis, and its background estimation strategy. The systematic uncertainties include experimental and theoretical uncertainties. Experimental uncertainties may include uncertainties in the ab- – 24 – solute jet and ET miss energy scales and resolutions, the jet quality requirements, pile-up corrections, b-tagging efficiencies, the soft contributions to ETmiss and the luminosity. Un- certainties in lepton identification and reconstruction efficiencies, energy/momentum scale and resolution are included for events with selected or vetoed leptons. Uncertainties due to the finite statistics of the background MC samples and others related to the modelling of the background processes are also included in the analyses. The signal modelling is subject to experimental and theoretical uncertainties. The experimental uncertainties are the same as for the background processes. Theoretical uncertainties affecting the production cross-section (normalisation) and the acceptance are JHEP05(2019)142 considered separately. The strategy used to estimate systematic uncertainties for those signal models studied in this paper which are not discussed in previous publications is outlined below. The results for the 2HDM+a and DE signal models include theoretical systematic un- certainties due to parton distribution functions (PDFs), evaluated following the PDF4LHC recommendations [202]. The choice of different PDFs results in up to 2% uncertainty in the acceptance and up to 10% uncertainty in the cross-section. Uncertainties related to the choice of renormalisation and factorisation scales are derived by varying independently such scales by a factor of 2.0 and 0.5 relative to the nominal values used for the MC generation. They account for an uncertainty in the acceptance below 5% for the differ- ent analyses. Uncertainties in initial- and final-state radiation due to the parton shower modelling are estimated by generating MC samples with alternative underlying event and multi-parton interaction parameter choices resulting in uncertainties between 5% and 15% in the signal acceptance, typically increasing at higher mediator masses. In the very large jet multiplicity phase space of the tt̄tt̄ analysis they reach values of 50%. In some cases, additional uncertainties are included to account for non-closure effects of the rescaling procedure described in section 3. These uncertainties include a contribution from the statistical uncertainty associated with the acceptance ratios determined from the baseline signal sample. For the h(γγ) + ET miss (Z(``) + E miss ) analysis this translates in up T to 7% (8%) uncertainty in the final 2HDM+a signal yields. 6 Interpretation of the results This section summarises the exclusion limits set by ATLAS published searches briefly outlined in section 4, on the various signal models described in section 2 (following the notation in table 1). The analyses and corresponding signal regions are referred to by their analysis labels defined in tables 2 and 3. The observed and expected 95% confidence level (CL) exclusion limits are obtained from the signal region or combination of regions of each contributing analysis using the CLs [203] method. The signal contamination in CRs across different analyses are kept minimal through dedicated selection requirements and hence are not explicitly taken into account in the following results. In section 6.3.1 a statistical combination of the h + ET miss final states is used to derive the results. – 25 – 1 q g ATLAS s = 13 TeV, 3.6-37.0 fb−1 95% CL upper limits Observed Γ/m Z'=0.15 Expected Γ/m Z'=0.1 0.5 Dijet 8 TeV Γ/m Z'=0.07 −1 0.4 20.3 fb Phys. Rev. D 91, 052007 (2015) Boosted dijet + ISR Di-b-jet trigger 0.3 −1 36.1 fb (Preliminary) arXiv: 1801.08769 Resolved dijet + ISR (γ ) −1 Preliminary, 15.5 fb 0.2 ATLAS-CONF-2016-070 Resolved dijet + ISR (j) Jet trigger Preliminary, 15.5 fb −1 ATLAS-CONF-2016-070 (Preliminary) Dibjet −1 24.3 & 36.1 fb Phys. Rev. D 98 (2018) 032016 0.1 Dijet TLA JHEP05(2019)142 −1 3.6 & 29.7 fb Phys. Rev. Lett. 121 (2018) 081801 tt resonances −1 36.1 fb Eur. Phys. J. C 78 (2018) 565 Axial vector mediator |y*12| < 0.3 Dijet 0.05 Dirac DM |y*12| < 0.6 −1 37.0 fb Phys. Rev. D 96, 052004 (2017) mχ = 10 TeV, gχ = 1.0 0.04 Dijet angular −1 37.0 fb Phys. Rev. D 96, 052004 (2017) 0.03 100 200 1000 2000 mZ' [GeV] A Figure 10. Dijet search contours for 95% CL upper limits on the coupling gq as a function of 0 the resonance mass mZA0 for the leptophobic axial-vector ZA model. The expected limits from each search are indicated by dotted lines. For illustrative purpose, the dijet + ISR Preliminary searches are shown in the plot. The TLA dijet analysis has two parts, employing different datasets with different selections in the rapidity difference y ∗ as indicated. The yellow contour shows the results of the dijet search using 20.3 fb−1 of 8 TeV data. Coupling values above the solid lines are excluded, as long as the signals are narrow enough to be detected using these searches. The TLA dijet search with |y ∗ | < 0.6 is sensitive up to Γ/mZ 0 = 7%, the TLA dijet with |y ∗ | < 0.3 and dijet + ISR searches are sensitive up to Γ/mZ 0 = 10%, and the dijet and dibjet searches are sensitive up to Γ/mZ 0 = 15%. The dijet angular analysis is sensitive up to Γ/mZ 0 = 50%. No limitation in sensitivity arises from large width resonances in the tt̄ resonance analysis. Benchmark width lines are indicated in the canvas. The Γ/mZ 0 = 50% lies beyond the canvas borders. 6.1 Vector or axial-vector dark matter models 6.1.1 Neutral interaction The V/AV simplified model is strongly constrained by searches for a high-mass resonance decaying into a pair of fermions and searches for associated production of DM particles with an ISR object. As presented in figure 10 for the case of an axial-vector mediator, each resonance search analysis is sensitive to complementary regions of the mass-coupling parameter space. Couplings above the exclusion line are excluded, as long as the width predicted by the model is smaller than the maximal ratio of width to mediator mass (Γ/mZ 0 ) to which the analysis is sensitive. This limitation arises where the background model is estimated via a sliding-window fit of the mjj distribution. Specifically, the TLA dijet analysis assuming |y ∗ | < 0.6 is sensitive up to around Γ/mZ 0 = 7%, the TLA dijet analysis requiring |y ∗ | < 0.3 and the boosted dijet+ISR analysis are sensitive up to around Γ/mZ 0 = 10%, while the dijet and dibjet analyses are sensitive up to around Γ/mZ 0 = 15%. Finally, the dijet – 26 – 1.6 mχ [TeV] Dijet Dijet s = 13 TeV, 37.0 fb-1 PRD 96, 052004 (2017) ATLAS 1.4 Dijet TLA s = 13 TeV, 29.3 fb-1 PRL 121 (2018) 0818016 Dijet + ISR s = 13 TeV, 15.5 fb-1 Preliminary ATLAS-CONF-2016-070 1.2 ' mZ V tt resonance = 1 mχ e s = 13 TeV, 36.1 fb-1 × nc Dibjet 2 ona .12 EPJC 78 (2018) 565 es =0 tt r 2 h Dibjet 0.8 lic Ωc e s = 13 TeV, 36.1 fb-1 lR JHEP05(2019)142 Dijet a PRD 98 (2018) 032016 erm 0.6 Th Emiss T +X miss ET +γ s = 13 TeV, 36.1 fb-1 Eur. Phys. J. C 77 (2017) 393 0.4 miss ET +jet s = 13 TeV, 36.1 fb-1 JHEP 1801 (2018) 126 Emiss T +X miss +Z(ll) s = 13 TeV, 36.1 fb-1 Vector mediator, Dirac DM ET 0.2 gq = 0.25, g = 0, gχ = 1 PLB 776 (2017) 318 miss -1 l E T +V(had) s = 13 TeV, 36.1 fb All limits at 95% CL JHEP 10 (2018) 180 0 0.5 1 1.5 2 2.5 3 3.5 mZ'V [TeV] (a) 1.6 mχ [TeV] Dilepton s = 13 TeV, 36.1 fb-1 ATLAS JHEP 10 (2017) 182 1.4 Dijet ' Dijet s = 13 TeV, 37.0 fb-1 mZ V 1.2 = PRD 96, 052004 (2017) mχ 2 Dijet TLA s = 13 TeV, 29.3 fb-1 × 1 2 0. PRL 121 (2018) 0818016 2 = h 1 Ω c lic Re Emiss al T +X m er miss -1 ET +γ s = 13 TeV, 36.1 fb 0.8 Th Eur. Phys. J. C 77 (2017) 393 miss -1 ET +jet s = 13 TeV, 36.1 fb JHEP 1801 (2018) 126 0.6 Dijet Dilepton 0.4 Emiss Vector mediator, Dirac DM 0.2 T +X gq = 0.1, g = 0.01, gχ = 1 l All limits at 95% CL 0 0.5 1 1.5 2 2.5 3 3.5 mZ'V [TeV] (b) Figure 11. Regions in a (mediator-mass, DM-mass) plane excluded at 95% CL by dijet, dilepton miss and ET +X searches, for leptophobic (a) or leptophilic (b) vector mediator simplified models described in section 2.1.1. The exclusions are computed for a DM coupling gχ , quark coupling gq , universal to all flavours, and lepton coupling g` as indicated in each case. Dashed curves labelled “thermal relic” correspond to combinations of DM and mediator mass values that are consistent with a DM density of Ωh2 = 0.12 and a standard thermal history as computed in MadDM [77, 204]. Above the curve in (a) annihilation processes described by the simplified model deplete Ωh2 to below 0.12. In (b), this occurs between the two dashed curves. The dotted line indicates the kinematic threshold where the mediator can decay on-shell into DM. – 27 – 1.6 mχ [TeV] Dijet Dijet s = 13 TeV, 37.0 fb-1 PRD 96, 052004 (2017) ATLAS 1.4 Dijet TLA s = 13 TeV, 29.3 fb-1 PRL 121 (2018) 0818016 Dijet + ISR s = 13 TeV, 15.5 fb-1 Preliminary ATLAS-CONF-2016-070 1.2 ' 1 2 = mZ A 0. h 2 = tt resonance mχ 1 × Ωc s = 13 TeV, 36.1 fb-1 2 eli c e R nc EPJC 78 (2018) 565 al na er m e so Dibjet 0.8 Th tt r s = 13 TeV, 36.1 fb-1 PRD 98 (2018) 032016 JHEP05(2019)142 0.6 Emiss T +X rity Dibjet miss nita ET +γ s = 13 TeV, 36.1 fb-1 Dijet Eur. Phys. J. C 77 (2017) 393 eU 0.4 miss ET +jet s = 13 TeV, 36.1 fb-1 iv bat JHEP 1801 (2018) 126 miss +Z(ll) s = 13 TeV, 36.1 fb-1 Axial-vector mediator, Dirac DM rtur Emiss ET 0.2 T +X PLB 776 (2017) 318 Pe gq = 0.25, g = 0, gχ = 1 miss ET +V(had) s = 13 TeV, 36.1 fb -1 l All limits at 95% CL JHEP 10 (2018) 180 0 0.5 1 1.5 2 2.5 3 3.5 mZ'A [TeV] (a) 1.6 mχ [TeV] Dilepton s = 13 TeV, 36.1 fb-1 ATLAS JHEP 10 (2017) 182 1.4 Dijet ' Dijet s = 13 TeV, 37.0 fb-1 mZ A 1.2 = PRD 96, 052004 (2017) mχ × Dijet TLA s = 13 TeV, 29.3 fb-1 2 1 2 PRL 121 (2018) 0818016 0. 1 2 = c h Ω lic Emiss T +X Re miss -1 0.8 al ET +γ s = 13 TeV, 36.1 fb e rm Eur. Phys. J. C 77 (2017) 393 Th miss E T +jet s = 13 TeV, 36.1 fb -1 JHEP 1801 (2018) 126 0.6 ity r nita eU 0.4 Dijet iv bat Dilepton Axial-vector mediator, Dirac DM rtur 0.2 Pe gq = 0.1, g = 0.1, gχ = 1 Emiss T +X l All limits at 95% CL 0 0.5 1 1.5 2 2.5 3 3.5 mZ'A [TeV] (b) Figure 12. Regions in a (mediator-mass, DM-mass) plane excluded at 95% CL by visible and invisible searches, for leptophobic (a) or leptophilic (b) axial-vector mediator simplified models described in section 2.1.1. The exclusions are computed for a DM coupling gχ , quark coupling gq , universal to all flavours, and lepton coupling g` as indicated in each case. Dashed curves labelled “thermal relic” correspond to combinations of DM and mediator mass values that are consistent with a DM density of Ωh2 = 0.12 and a standard thermal history, as computed in MadDM [77, 204]. Between the two curves, annihilation processes described by the simplified model deplete Ωh2 to below 0.12. A dotted line indicates the kinematic threshold where the mediator can decay on- shell into DM. Excluded regions that are in tension with the perturbative unitary considerations of ref. [205] are indicated by shading in the upper left corner. – 28 – angular analysis is sensitive up to Γ/mZ 0 = 50%. No limitation in sensitivity arises from large width resonances in the tt̄ resonance analysis, as the background is constrained in dedicated control regions. The different dijet analyses (see section 4.2 for details) are sensitive to different mass regimes as well as coupling values. For illustrative purpose, the dijet + ISR Preliminary searches are shown in the plot, as they constraint a unique portion of the parameter space. At the time of writing, a dijet + ISR analysis based on 80 fb −1 of integrated luminosity was published [206], which also probes a similar parameter space. The boosted dijet+ISR analysis has the best reach for low masses, excluding ZA 0 mediator masses between 100 GeV and 220 GeV. Two new interpretations, for the dibjet and tt̄ resonance analyses, are presented for these models. The dibjet (tt̄ resonance) analysis JHEP05(2019)142 places constraints on ZA0 mediators with masses between 500 GeV and 2.5 (2) TeV, in the same region of sensitivity of the dijet, TLA dijet, and boosted dijet+ISR analyses. To illustrate the complementarity of the searches [75, 77], three different coupling scenarios are also considered in the interpretation of the results: 0 /Z 0 ); Scenario 1 gq = 0.25, g` = 0, gχ = 1 (leptophobic ZV A 0 ); Scenario 2 gq = 0.1, g` = 0.01, gχ = 1 (leptophilic ZV 0 ). Scenario 3 gq = 0.1, g` = 0.1, gχ = 1 (leptophilic ZA In particular, the lower lepton coupling value is set to highlight the dilepton search sensi- tivity even for very small values of this parameter. The exclusions from the resonance searches (dijet, dibjet, dilepton) in the (mZ 0 , mχ ) V/A plane are derived from the limits placed on resonances reconstructed with a Gaussian shape, while the limits from the ET miss +X and tt̄ resonance analyses are derived using a mixture of simulated signal samples and rescaling procedures as described in section 3. For each scenario in figures 11 and 12, dashed curves labelled “thermal relic” correspond to combinations of DM and mediator mass values that are consistent with a DM density of Ωh2 = 0.12 and a standard thermal history, as computed in MadDM [77, 204]. Between the two curves, annihilation processes described by the simplified model deplete the relic density to below the thermal value (except for figure 11a, where this occurs above the dashed curve). A dotted line indicates the kinematic threshold where the mediator can decay on-shell into DM particles. Excluded regions that are in tension with the perturbative unitary considerations of ref. [205] are indicated by shading in figure 12. The sensitivity reach of the various experimental signatures for the leptophobic vector- mediator scenario as a function of the DM and mediator masses is summarised in figure 11a. Since the chosen universal quark coupling is relatively high in comparison with other bench- marks, the strongest limits are obtained from the resonance searches. These analyses are sensitive to mediator masses between 200 GeV and 2.5 TeV with little dependence on the DM mass. Opening of the ZV 0 → χχ̄ decay channel, significantly reduces the sensitivity observed at high mediator masses and for 200 < mZV0 < 450 GeV when mZV0 > 2mχ . The boosted dijet + ISR search is not reinterpreted here but has sensitivity in this region. The lower limit on the mass is determined by the trigger requirements of the resolved dijet + ISR analysis. For mZV0 < 2mχ , masses up to 2.9 TeV are excluded by the resolved dijet + – 29 – ISR, dijet TLA and dijet searches. Compared to the dijet searches, the tt̄ resonance anal- ysis is particularly sensitive to the reduction in effective cross-section related to changes of the branching ratio, as can be inferred from the coupling reach of figure 10. Conversely, the sensitivity of the ET miss +X signatures is highest in the region m 0 > 2m , up to ZV χ mediator masses of 1.5 TeV and provides unique coverage for masses below 500 GeV. The sensitivity of these analyses is strongly decreased for mZV0 < 2mχ , where the DM particles are produced off-shell, with a consequent strong reduction of the production cross-section. For this reason, only the jet+ET miss and γ + E miss analyses can probe the off-shell regime T for this benchmark scenario, and only in the case of very low mediator and DM masses. It is important to highlight that if the value chosen for gq were reduced, the relative interplay JHEP05(2019)142 between the dijet and ET miss +X searches would change, as exemplified by the change of the dijet limit in the different coupling scenarios described in the following. The experimental limits for the leptophilic vector-mediator model are summarised in figure 11b. In this case, the mediator decay rates into quarks are reduced in favour of a higher branching ratio to DM particles, reducing the sensitivity of dijet searches to this sce- nario, whereas the leptonic branching ratio allows dilepton searches to impose constraints on a wide range of mediator masses. The gap in sensitivity of dijet searches around mediator masses of about 1.7 TeV is due to statistical fluctuation in the dijet spectrum. This bench- mark highlights the complementarity among dijet, dilepton, and ET miss +X final states. In this case, dibjet and tt̄ resonance searches are not included in the final result. The reso- nance searches exclude mediator masses between 150 GeV and 2 TeV (except for a small gap around 1.7 TeV), if mZV0 < 2mχ and between 150 and 350 GeV for all DM masses. Com- plementarily, the ET miss +X searches exclude mediator masses up to 1 TeV for m 0 > 2m . ZV χ Similar considerations can be made for the axial-vector mediator models, presented in figure 12, with the exception that in the presence of non-vanishing coupling to leptons (leptophilic scenario), the dilepton resonance search becomes by far the most sensitive analysis for this model, excluding the mass range 150 GeV < mZA0 < 2.8 TeV for any DM mass. Also in this case, the sensitivity of this analysis increases when the ZA 0 → χχ̄ is kinematically forbidden and becomes independent of the DM mass above threshold. For mZA0 < 2mχ , masses up to 3.5 TeV are excluded. Collider experiments provide an approach to DM searches which is complementary to direct and indirect detection experiments [76]. It is therefore interesting and informative, though model-dependent, to compare the V/AV limits with the results from other DM searches. Figure 13 shows the translation of the V/AV model limits into limits on the spin-dependent χ-proton and spin-independent χ-nucleon scattering cross-sections as a function of the DM mass. The direct detection experiments dominate the sensitivity by a few orders of magnitude for DM masses above 10 GeV, thanks to coherence effects, the spin-independent interaction cross-section with heavy nuclei is enhanced by A2 , where A is the number of nucleons in a nucleus. However, with the assumed coupling strengths, the analyses presented in this paper complement direct detection limits in the low DM mass range where the direct DM search experiments have less sensitivity due to the very low energy recoils that such low-mass DM particles would induce. The lower edge of the sensitivity contour for all analyses in figure 13a (figure 13b) is driven by the high-mass – 30 – − 37 10 σSI (χ-nucleon) [cm2] Dijet − 38 Dijet s = 13 TeV, 37.0 fb-1 10 ATLAS PRD 96, 052004 (2017) Dijet TLA s = 13 TeV, 29.3 fb-1 PRL 121 (2018) 0818016 − 39 10 Dijet + ISR s = 13 TeV, 15.5 fb -1 tt resonance ATLAS-CONF-2016-070 (Preliminary) − 40 tt resonance 10 CRESST III Emiss T +X s = 13 TeV, 36.1 fb-1 EPJC 78 (2018) 565 − 41 Dibjet Dibjet 10 s = 13 TeV, 36.1 fb-1 Dijet PRD 98 (2018) 032016 10− 42 Emiss +X DarkSide-50 T miss ET +γ s = 13 TeV, 36.1 fb-1 − 43 Eur. Phys. J. C 77 (2017) 393 10 miss ET +jet s = 13 TeV, 36.1 fb-1 JHEP 1801 (2018) 126 miss ET +Z(ll) s = 13 TeV, 36.1 fb-1 JHEP05(2019)142 10−44 PLB 776 (2017) 318 aX LUX miss ET +V(had) s = 13 TeV, 36.1 fb-1 − 45 Pand JHEP 10 (2018) 180 10 N1T CRESST III XENO arXiv:1904.00498 − 46 10 XENON1T PRL 121, 111302 (2018) Vector mediator, Dirac DM − 47 PandaX 10 gq = 0.25, g = 0, gχ = 1 l PRL 117, 121303 (2016) ATLAS limits at 95% CL, direct detection limits at 90% CL DarkSide-50 − 48 PRL 121, 081307 (2018) 10 2 3 1 10 10 10 LUX PRL 118, 021303 (2017) mχ [GeV] (a) − 37 10 σSD (χ-proton) [cm2] Dilepton s = 13 TeV, 36.1 fb-1 JHEP 10 (2017) 182 10 − 38 ATLAS PICO-60 C3F8 Dijet − 39 Dijet s = 13 TeV, 37.0 fb-1 10 PRD 96, 052004 (2017) Dijet TLA s = 13 TeV, 29.3 fb-1 PRL 121 (2018) 0818016 − 40 10 Emiss T +X E miss T +γ s = 13 TeV, 36.1 fb-1 10−41 Eur. Phys. J. C 77 (2017) 393 miss E T +jet s = 13 TeV, 36.1 fb-1 JHEP 1801 (2018) 126 10−42 Emiss Dijet PICO-60 C3F8 T +X PRL 118, 251301 (2017) − 43 10 10−44 Dilepton − 45 Axial-vector mediator, Dirac DM 10 gq = 0.1, g = 0.1, gχ = 1 l ATLAS limits at 95% CL, direct detection limits at 90% CL − 46 10 3 1 10 102 10 mχ [GeV] (b) Figure 13. A comparison of the inferred limits with the constraints from direct detection experi- ments on (a) the spin-dependent WIMP-proton scattering cross-section in the context of the vector leptophobic model and (b) the spin-independent WIMP-nucleon scattering cross-section in the con- text of the axial-vector leptophilic model. The results from this analysis, excluding the region inside or to the left of the contour, are compared with limits from direct detection experiments. ATLAS limits are shown at 95% CL and direct detection limits at 90% CL. ATLAS searches and direct detection experiments exclude the shaded areas. Exclusions beyond the canvas are not implied for miss the ATLAS results. The dijet and ET +X exclusion regions represent the union of exclusions from all analyses of that type. – 31 – reach of each analysis in figure 11a (12b), as the scattering cross-section limit is inversely proportional to the mediator mass reach (raised to the fourth power). Conversely, the upper edge of the scattering cross-section contour for the dijet and dilepton analyses is driven by their low-mass sensitivity limit due to the trigger requirements employed in these analyses. Further details of this comparison are discussed in appendix B. 6.1.2 Baryon-charged interaction In the context of the VBC model, the results from the h(γγ)+ET miss and h(bb̄)+E miss analy- T 0 ses are interpreted in the plane formed by the ZB and DM masses, due to the characteristic JHEP05(2019)142 signature of this model involving Higgs-strahlung from the ZB0 mediator. The h(bb̄) + ET miss interpretation was developed subsequently to the original publication [23]. The results are shown in figure 14 in the (mZB0 , mχ ) plane for gq = 1/3, gχ = 1 and sin θ = 0.3. The dashed lines indicate the expected exclusion contours from the two separate channels and their combination (based on best expected limits), while the black solid line shows the observed exclusion, presented only for the combined result. The band around the expected com- bined contour shows the effect of one-standard-deviation variation of the total systematic uncertainties. The h(bb̄)+ET miss analysis sets the strongest bounds in this model, excluding mediator masses up to 1.9 TeV for all DM mass hypotheses for which the mediator invisible decay is kinematically allowed. Due to the lower branching ratio, the h(γγ) + ET miss is less sensitive to this model for high mediator masses, but it is competitive for mZB0 < 50 GeV thanks to the higher acceptance of the analysis which can trigger on the photons instead of the ET miss and its smaller systematic uncertainties compared to the h(bb̄) + E miss analysis. T mχ [TeV] miss ATLAS h+ET observed miss s = 13 TeV, 36.1 fb-1 h+ET expected ±1σ 10 h(bb)+E miss expected All limits at 95 % CL T PRL 119 (2017) 181804 Z'B, Dirac DM miss h(γ γ )+E expected gχ=1 gq=1/3 g =mZ'B T Z'B PRD 96 (2017) 112004 1 sin(θ)=0.3 10−1 =2 mχ m Z' B 10−2 10−3 −2 10 10−1 1 10 mZ'B [TeV] Figure 14. Exclusion contours for the VBC model in the (mZB0 , mχ ) plane for gq = 1/3, gχ = 1 and sin θ = 0.3. The dashed lines indicate the expected exclusion contours from the two separate channels and their combination, while the solid line shows the observed exclusion, presented only for the combined result. The band around the expected combined contour shows the effect of a one-standard-deviation variation of the total systematic uncertainties. At high mediator masses, miss the combined exclusion fully overlaps with the exclusion from the h(bb̄) + ET analysis. – 32 – 6.1.3 Neutral flavour-changing interaction For the VFC models, expected and observed limits from the t + ET miss and same-sign tt analyses are derived for each independent subprocess leading to the two signatures, as de- scribed in section 2.1.3 and schematically summarised in figures 2b–2d. These individual results are converted into limits for the complete VFC model following the rescaling pro- cedure described in section A.2. These results were obtained subsequently to the original analyses publications. The sensitivity of the experimental analyses to this model is explored in three scenarios that investigate different interpretation variables (where B is the invisible branching ratio JHEP05(2019)142 of the mediator): Scenario 1 (mZVFC 0 , gut ) interpretation plane, assuming gχ = 0.5 or gχ = 1.0. Scenario 2 (B(χχ̄), gut ) interpretation plane, assuming mZVFC 0 = 1 TeV. Scenario 3 (gχ , gut ) interpretation plane, assuming mZVFC 0 = 1 TeV. The first scenario, presented in figure 15, directly identifies the constraints on the main parameters of the model. The two different gχ coupling values highlight the different contributions of the invisible final state (t + ETmiss ), which probes g ut values down to 0.7 for 1 TeV mediators and can exclude couplings down to 0.13 for 1.5 TeV mediators when the DM coupling is set to unity. In this scenario the visible final state (tt) constrains couplings down to 0.3 for mediator masses up to 3 TeV and it is relatively independent of gχ . This is due to the fact that the sensitivity of this final state is dominated by the t-channel exchange of the mediator and therefore it is sensitive to gχ only through the total width of the mediator. In this result, only mediator masses above 1 TeV are under study. However, mediator masses down to 100 GeV are excluded by previous publications [207] for a coupling assumption of gq ∼ 3 · 10−2 . Limits are quite similar for the two DM coupling values for the same-sign tt analysis. 0 The sensitivity of this final state is dominated by the t-channel exchange of ZVFC especially for the values of gut which are probed. This process is sensitive to gχ only through the total with of the mediator involved in the propagator, and therefore does not change drastically when gχ is varied. The second and third scenarios, presented in figure 16, further highlight the comple- mentarity between the visible and invisible final states as a function of the couplings and the invisible branching ratio of the mediator. Couplings of the ZVFC 0 mediator to SM fermions can be excluded down to 0.14 for any value of gχ or B(χχ̄). – 33 – 0.5 0.5 gut gut ATLAS ATLAS 0.45 -1 0.45 s = 13 TeV, 36.1 fb s = 13 TeV, 36.1 fb-1 0.4 0.4 0.35 0.35 0.3 0.3 0.25 0.25 0.2 VFC, Dirac DM 0.2 VFC, Dirac DM Limits at 95% CL Limits at 95% CL 0.15 Obs 0.15 Obs mχ=1 GeV, gχ=0.5 Exp mχ=1 GeV, gχ=1.0 Exp 0.1 0.1 Same-sign tt [JHEP 12 (2018) 039] Same-sign tt [JHEP 12 (2018) 039] 0.05 t+ET miss [arXiv:1812.09743] 0.05 miss t+ET [arXiv:1812.09743] 0 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 JHEP05(2019)142 mZ'VFC [TeV] mZ'VFC [TeV] (a) (b) miss Figure 15. Exclusion regions in the (mZVFC0 , gut ) plane from the t+ET and same-sign tt analyses for the VFC model. The observed exclusion is indicated for each of the two analyses by the filled area. The mass of the DM particle is set to 1 GeV and the DM coupling, gχ , is set to (a) 0.5 or (b) 1. 0.25 0.22 gut gut ATLAS 0.2 ATLAS s = 13 TeV, 36.1 fb-1 s = 13 TeV, 36.1 fb-1 0.2 0.18 0.16 0.14 0.15 0.12 0.1 0.1 0.08 mχ=1 GeV, mZ' =1 TeV 0.06 mχ=1 GeV, mZ' =1 TeV 0.05 VFC Same-sign tt [JHEP 12 (2018) 039] VFC, Dirac DM 0.04 VFC Same-sign tt [JHEP 12 (2018) 039] VFC, Dirac DM miss Limits at 95% CL miss Limits at 95% CL t+ET [arXiv:1812.09743] t+ET [arXiv:1812.09743] (Γ/m) ≥ 0.2 Obs 0.02 (Γ/m) ≥ 0.2 Obs Z'VFC Exp Z'VFC Exp 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.5 1 1.5 2 2.5 3 B(χχ) gχ (a) (b) miss Figure 16. Exclusion limits from the t + ET and same-sign tt analyses for the VFC model as a function of the SM coupling gut and (a) the DM branching ratio or (b) the DM coupling gχ . The observed exclusion is indicated for each of the two analyses by the filled area. The mass of the DM 0 particle is set to 1 GeV and the mass of the ZVFC boson is set to 1 TeV. The dark shaded area corresponds to an invisible partial width of the mediator above 20%. 6.2 Scalar or pseudo-scalar dark matter models 6.2.1 Colour-neutral interaction The most stringent limits on S/PS models are obtained from tt̄ +ET miss final states, which are studied in three channels assuming fully-hadronic, semileptonic and fully-leptonic top pair decays, respectively. The fully leptonic channel excludes scalar-mediator models with unitary couplings gχ = gq = g = 1 up to mediator masses of 45 GeV, setting in this mass range the strongest upper limits on the ratio of the signal production cross-section to the nominal cross-section (signal strength or σ/σ(g = 1.0)), as shown in figure 17a. In the case – 34 – of pseudo-scalar mediator models (figure 17b), similar sensitivity is obtained by all channels and mediator masses in the range 15–25 GeV are excluded. In all cases, a DM mass of 1 GeV is assumed, but the results are valid for all DM mass choices for which the mediator’s decay into a pair of DM particles is kinematically allowed (mφ/a > 2mχ ). Pseudo-scalar mediator models can also be constrained by jet+ET miss final states, where the mediator is produced through loop-induced gluon fusion. Although the limits obtained by this signature are not competitive with the tt̄ +ET miss final state, except in the mass range above 300 GeV, they provide a complementary constraint, which would become particularly important in case of a discovery. For the scalar model, the jet+ET miss final-states cross-section is instead too small to be probed. Ditop resonance searches in final states with two or four tops can also JHEP05(2019)142 constrain this parameter space for mφ/a > 2mt . However, tt̄ production through a spin-0 resonance presents a strong interference pattern with SM top pair production [208], which needs to be treated with care. On the other hand, four-top final states are characterised by relatively low event yields with the currently available integrated luminosity. For these reasons the study of these final states is not considered here. Finally, bb̄ +ET miss final states are also used to set constraints on these simplified models, resulting in upper limits on the signal strength between 200 and 300 for mediator masses below 100 GeV. These results quantify the sensitivity to these models if up-type couplings are suppressed. – 35 – σ/ σ(g=1) ATLAS 103 s = 13 TeV, 36.1 fb-1 102 Observed All limits at 95% CL Expected miss JHEP05(2019)142 ET +bb 0L [EPJC 78 (2018) 18] Scalar φ, φ → χχ miss ET +tt 0L [EPJC 78 (2018) 18] 10 g = gq= gχ = 1 miss ET +tt 1L [JHEP 06 (2018) 108] miss mχ = 1 GeV, Dirac DM ET +tt 2L [EPJC 78 (2018) 18] 1 20 30 40 50 100 200 300 mφ [GeV] (a) σ/ σ(g=1) ATLAS s = 13 TeV, 36.1 fb-1 103 102 All limits at 95% CL Observed Expected Pseudo-scalar a, a → χχ miss ET +bb 0L [EPJC 78 (2018) 18] miss g = gq= gχ = 1 ET +tt 0L [EPJC 78 (2018) 18] miss ET +tt 1L [JHEP 06 (2018) 108] 10 mχ = 1 GeV, Dirac DM miss ET +tt 2L [EPJC 78 (2018) 18] miss ET +jet [JHEP 01 (2018) 126] 1 20 30 40 50 100 200 300 ma [GeV] (b) Figure 17. Exclusion limits for (a) colour-neutral scalar or (b) pseudo-scalar mediator models as a function of the mediator mass for a DM mass of 1 GeV. The limits are calculated at 95% CL and are expressed in terms of the ratio of the excluded cross-section to the nominal cross-section for a coupling assumption of g = gq = gχ = 1. The solid (dashed) lines show the observed (expected) exclusion limits for each channel. – 36 – 6.2.2 Colour-charged interaction The strongest exclusion limits on colour-charged mediators ηq that couple to first- and second-generations left-handed quarks are set by the jet+ET miss analysis. Assuming a uni- tary coupling, ηq mediator masses up to 1.7 TeV are excluded for mχ = 50 GeV. Further- more, ηq mediator masses below 600 GeV are excluded for all DM masses such that the decay ηq → qχ is kinematically allowed. The strongest exclusion limits on colour-charged mediators ηb that couple to third-generation right-handed b-quarks are set by the b + ET miss analysis. Assuming a coupling set to the value that yields a relic density value consistent with astrophysical observations, masses up to 1.4 TeV are excluded for mχ = 1 GeV. Fi- JHEP05(2019)142 nally, t+ETmiss final states are used to constrain the colour-charged mediator’s η coupling to t right-handed top quarks. Mediator masses up to 3.4 TeV are excluded, assuming a 10 GeV DM particle mass and setting the coupling strengths of this model to: λt = 0.4 and gs = 0.2. 6.3 Extended Higgs sector dark matter models 6.3.1 Two-Higgs-doublet models with a vector mediator The 2HDM+ZV 0 model is constrained by the h(bb̄) + E miss and h(γγ) + E miss analyses. T T The results are interpreted in terms of exclusion limits in the (mA , mZV0 ) plane shown in figure 18. The statistical combination of the two analyses is also presented. Masses of the pseudo-scalar A in the range 200–600 GeV are excluded for mZV0 = 1.5 TeV. The limit in sensitivity is driven by the fact that the A → χχ̄ branching ratio decreases with increasing mA due to decay channels involving top quarks or other heavy bosons of the extended Higgs sector becoming accessible (tt̄, HZ and W ± H ∓ ). At higher mZV0 the loss in branching ratio is combined with the smaller production cross-section so that the reach of the analysis is limited to smaller pseudo-scalar masses. For mA < 2mt and mA > 2mχ , there are no more competing decay channels and the reach of the analysis does not depend on mA any longer. This creates the turnover in the exclusion contour for mZV0 = 2.5 TeV. The two h+ET miss decay signatures are highly complementary at low Z 0 masses, as can V be observed in the enlarged inset in the figure, while the h(bb̄) + ETmiss analysis dominates the sensitivity at high ZV 0 masses. Due to this complementarity, the gain obtained by the statistical combination of the two signatures is limited to the low mass region for this model. – 37 – 1200 mA [GeV] 500 ATLAS 1100 s = 13 TeV, 36.1 fb-1 450 400 1000 All limits at 95 % CL 350 2HDM+Z'V, Dirac DM 900 tanβ = 1, g = 0.8, mχ = 100 GeV Z'V 300 250 mH = mH± = 300 GeV 800 200 300 400 500 600 700 800 900 h -m miss 700 h+ET observed miss V h+ET expected ±1σ Z' m miss 600 h(bb)+E expected m = T PRL 119 (2017) 181804 A miss 500 h(γ γ )+E T expected PRD 96 (2017) 112004 400 300 JHEP05(2019)142 200 500 1000 1500 2000 2500 3000 3500 mZ' [GeV] V 0 Figure 18. Exclusion contours for the 2HDM+ZV scenario in the (mZV0 , mA ) plane for tan β = 1, gZV0 = 0.8 and mχ = 100 GeV. The dashed lines indicate the expected exclusion contours from the two separate channels and their statistical combination, while the black solid line shows the observed exclusion, presented only for the combined result. The band around the expected combined contour shows the effect of a one-standard-deviation variation of the total systematic uncertainties. The sharp turn in the exclusion contour for mZV0 = 2.5 GeV is given by the opening A decay channels competing with the considered final state for mA > 2mt . For this reason the exclusion sensitivity does not depend on mA below threshold. The inset in the top-right side of the panel shows a zoomed-in version of the result for low mZV0 masses to highlight the complementarity between the miss miss h(bb̄) + ET and the h(γγ) + ET analyses in this parameter region. 6.3.2 Two-Higgs-doublet models with a pseudo-scalar mediator As highlighted in section 2.3.2, the 2HDM+a model is characterised by a rich phenomenol- ogy. Constraints on this model from ATLAS searches are presented in this paper. Four different benchmark scenarios are used to evaluate the sensitivity to this model achieved by the Z/h+ET miss , tt̄/bb̄+E miss , h(inv), and tt̄tt̄ analyses. These four benchmark scenarios [78] T are consistent with bounds from electroweak precision, flavour and Higgs observables and are chosen to highlight the complementarity of the various final states. These scenarios rep- resent two-dimensional and one-dimensional scans of a five-dimensional parameter space, used to present the exclusion limits. Scenario 1 (ma , mA ) exclusion plane assuming tan β = 1 and sin θ = 0.35; Scenario 2 (ma , tan β) exclusion plane assuming mA = 600 GeV and sin θ = 0.35; Scenario 3 sin θ exclusion scan assuming a) mA = 600 GeV , ma = 200 GeV and tan β = 0.5, 1 or 50; b) mA = 1000 GeV , ma = 350 GeV and tan β = 0.5 or 1; Scenario 4 mχ exclusion scan assuming mA = 600 GeV, ma = 250 GeV, tan β = 1, sin θ = 0.35. – 38 – 2000 mA [GeV] ATLAS Γ /ma > 20% Emiss T +Z(ll) PLB 776 (2017) 318 -1 1800 s = 13 TeV, 36.1 fb 2HDM+a, Dirac DM Limits at 95% CL Observed mχ = 10 GeV, gχ = 1 1600 Emiss T +h(bb) Expected sinθ = 0.35, tanβ = 1 PRL 119 (2017) 181804 mA = mH = mH± 1400 Emiss T +h(γ γ ) 1200 PRD 96 (2017) 112004 JHEP05(2019)142 1000 Emiss T +Z(qq) 800 JHEP 10 (2018) 180 mA = 600 GeV 600 + mh h(inv) -1 s=7,8 TeV;4.7,20.3 fb mA = ma JHEP 11 (2015) 206, 400 mA = ma 200 100 150 200 250 300 350 400 ma [GeV] (a) tan β tttt ATLAS JHEP 09 (2017) 088 s = 13 TeV, 36.1 fb-1 Limits at 95% CL Observed Emiss T +Z(ll) Expected PLB 776 (2017) 318 2HDM+a, Dirac DM mχ = 10 GeV, gχ = 1 Emiss T +h(bb) mA = mH = mH± = 600 GeV PRL 119 (2017) 181804 sinθ = 0.35 1 Emiss T +h(γ γ ) tan β = 1 PRD 96 (2017) 112004 Emiss T +tt EPJC 78 (2018) 18 JHEP 06 (2018) 108 Γ /ma > 20% h(inv) s=7,8 TeV;4.7,20.3 fb-1 100 150 200 250 300 350 400 450 500 550 JHEP 11 (2015) 206, ma [GeV] (b) Figure 19. Regions in the (a) (ma , mA ) and (b) (ma , tan β) planes excluded by data at 95% CL by miss X + ET and tt̄tt̄ analyses, following the parameter choices of scenarios 1 and 2 of the 2HDM+a model. The dashed grey regions at the top of (a) and the bottom of (b) indicate the region where the width of any of the Higgs bosons exceeds 20% of its mass. The exclusion limits presented above conservatively neglect the contribution from bb̄-initiated production, which might be sizeable for miss miss tan β ≥ 3 for the Z + ET channel and, to a lesser extent, for the h + ET one. – 39 – In all cases, the masses of the heavy pseudo-scalar, heavy scalar, and charged bosons are kept equal (mA = mH = mH ± ). As visible in the results presented in figure 19a, the exclusion sensitivity is vastly dominated by the h(bb̄) + ET miss and Z(``) + E miss analyses T in the first scenario. These analyses are mostly sensitive to the production diagrams of figures 6d and 6e and their sensitivity depends on both pseudo-scalar mediator masses. The maximum reach is obtained for light pseudo-scalar ma up to 340 GeV, if the A boson mass is set to 1 TeV, while for ma = 150 GeV A boson masses between 280 GeV and 1.35 TeV are excluded. The combined contours of the h(bb̄) + ET miss and Z(``) + E miss analyses include T the h(γγ) + ET miss and Z(q q̄) + E miss exclusion areas, although the h(γγ) + E miss analysis T T still complements h(bb̄) + ET miss at low (m , m ) values. Finally, the h(inv) branching ratio JHEP05(2019)142 a A limit constrains very low values of ma for mA mass below 900 GeV and above 1.4 TeV, being sensitive only to the a boson production cross-section. In the context of 2HDM models, it is customary to investigate the sensitivity in terms of the tan β parameter. This is achieved in the second scenario presented in figure 19b. Although the exclusion reach is dominated also in this case by the h(bb̄) + ET miss and Z(``) + ET miss analyses, two additional signatures contribute at tan β ∼ 0.5: the tt̄ +E miss T and the tt̄tt̄ analyses. The sensitivity of the former analysis is driven by the production cross-section of the a mediator in association with a top-quark pair and it decreases when the decay of the light pseudo-scalar into a top-quark pair is kinematically allowed and competes with a → χχ̄. On the other hand, the sensitivity of the latter analysis is fairly independent of ma due to the contribution to the total four-top production cross-section from the heavy bosons H/A → tt̄, both of which have masses fixed to 600 GeV in this scenario. In the case of the h(bb̄) + ET miss analysis, the exclusion was not investigated below tan β = 0.5. Given the non-trivial dependency of the width on tan β in this channel, it is not possible to extrapolate beyond the area explored. Figures 20a and 20b present the exclusion limits dependence on the mixing angle, sin θ, for a low-mass and high-mass a hypothesis, as evaluated in the third scenario. The limits are expressed in terms of the ratio of the excluded cross-section to the nominal cross-section of the model. For scenario 3a (figure 20a), the lowest cross-section values are excluded by the Z(``) + ET miss and h(bb̄) + E miss analyses. The sensitivity of both Z + E miss analy- T T ses monotonically improves as a function of sin θ, as the cross-section of the non-resonant and resonant production diagrams, in figures 6d and 6e respectively, increases with sin θ. Conversely, the same production diagrams for the h + ET miss signatures have very different dependence on the mixing angle [152] in the two ma regimes explored here. The contribu- tion of each diagram is also affected by the different h(bb̄)+ET miss and h(γγ)+E miss analysis T selections. For this scenario, both analyses have maximum of sensitivity around sin θ ∼ 0.5. The three heavy-flavour signatures, bb̄ +ET miss , tt̄ +E miss and tt̄tt̄, are presented for dif- T ferent tan β assumptions. A value of tan β = 50 is studied for bb̄ +ET miss , with the aim of probing the parameter space where the coupling of the a mediator to down-type quarks is enhanced. However, the tt̄ +ET miss and tt̄tt̄ signatures are presented for tan β = 0.5 as they are not yet able to probe tan β values near unity. The tt̄tt̄ signature, in particular, shows a sin θ dependence complementary to the other signatures due to the combined contribu- tion of all neutral bosons decaying into top-quark pairs and is particularly sensitive at very – 40 – 102 σ/ σtheory Emiss +t t ATLAS 2HDM+a, Dirac DM T EPJC 78 (2018) 18 s = 13 TeV, 36.1 fb-1 mχ = 10 GeV, gχ = 1 JHEP 06 (2018) 108 Limits at 95% CL Observed ma = 200 GeV Emiss T +bb mA = mH = mH± = 600 GeV EPJC 78 (2018) 18 Expected miss 10 tanβ = 50: E +bb Emiss +h(bb) T T miss PRL 119 (2017) 181804 tanβ = 0.5: E +t t, tttt JHEP05(2019)142 T tanβ = 1: all others Emiss T +h(γ γ ) PRD 96 (2017) 112004 Emiss T +Z(ll) 1 PLB 776 (2017) 318 Emiss T +Z(qq) JHEP 10 (2018) 180 tttt 10− 1 JHEP 09 (2017) 088 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 sinθ (a) σ/ σtheory Emiss +t t ATLAS 2HDM+a, Dirac DM T EPJC 78 (2018) 18 s = 13 TeV, 36.1 fb-1 mχ = 10 GeV, gχ = 1 JHEP 06 (2018) 108 Limits at 95% CL 102 Observed ma = 350 GeV Emiss T +bb Expected mA = mH = mH± = 1 TeV EPJC 78 (2018) 18 miss tanβ = 50: E +bb Emiss +h(bb) T T miss PRL 119 (2017) 181804 tanβ = 0.5: E +t t, tttt T tanβ = 1: all others Emiss T +h(γ γ ) 10 PRD 96 (2017) 112004 Emiss T +Z(ll) PLB 776 (2017) 318 Emiss T +Z(qq) JHEP 10 (2018) 180 1 tttt JHEP 09 (2017) 088 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 sinθ (b) Figure 20. Observed exclusion limits for the 2HDM+a model as a function of sin θ, following the two parameter choices of scenario 3, (a) low-mass and (b) high-mass a hypotheses. The limits are calculated at 95% CL and are expressed in terms of the ratio of the excluded cross-section to the nominal cross-section of the model. – 41 – 108 104 σ/ σtheory Emiss Thermal Relic Density ATLAS s = 13 TeV, 36.1 fb-1 T +t t mχ = 0.5*ma EPJC 78 (2018) 18 7 3 10 2HDM+a, Dirac DM 10 JHEP 06 (2018) 108 mA = mH = mH± = 600 GeV Emiss +bb 6 2 10 sinθ = 0.35, gχ = 1 10 T EPJC 78 (2018) 18 ma = 250 GeV miss 105 tanβ = 50: ET +bb 10 tanβ = 0.5: E miss +tt Emiss T +h(bb) T PRL 119 (2017) 181804 104 tanβ = 1: all others 1 2 Thermal Relic Ω h = 0.12 103 10−1 Emiss T +h(γ γ ) PRD 96 (2017) 112004 102 10−2 Emiss T +Z(ll) −3 10 10 PLB 776 (2017) 318 Limits at 95% CL JHEP05(2019)142 σ/ σtheory=1 Observed 1 10−4 Emiss Expected T +Z(qq) JHEP 10 (2018) 180 10− 1 10 −5 50 100 150 200 250 300 350 400 450 relic density mχ [GeV] Figure 21. Observed exclusion limits for the 2HDM+a model as a function of mχ , following the parameter choices of scenario 4. The limits are calculated at 95% CL and are expressed in terms of the ratio of the excluded cross-section to the nominal cross-section of the model. The relic density for each mχ assumption is superimposed in the plot (long-dashed line) and described by the right vertical axis. For DM mass values where the relic density line is below Ωh2 = 0.12, the model depletes the relic density to below the thermal value. The two valleys at mχ = 125 GeV and mχ = 300 GeV determine the two a-funnel and A-funnel regions [78, 209, 210] where the predicted relic density is depleted by the resonant enhancement of the processes χχ̄ → A/a → SM. small mixing angles. Scenario 3b, presented in figure 20b, sets the mass of the light pseudo- scalar so that the a → tt̄ decay is kinematically allowed, which introduces an additional sin θ dependence to the X + ET miss analyses interpreted in this scenario. For this reason, the highest sensitivity for each analysis is found to be broadly around (or slightly below) the maximal mixing condition (θ = π/4), except for the tt̄tt̄ and h + ET miss signatures. The tt̄tt̄ signature shows a constant sensitivity as a function of sin θ (with an increase for very high values) due to the mass assumptions of this scenario (ma = 350 GeV and mA/H = 1 TeV) which cause the tt̄tt̄ production cross-section to be completely dominated by the tt̄ + a(tt) process. The h + ET miss signatures have a complex dependence on the mixing angle. This is due to the different contributions of resonant and non-resonant processes to the final selection in the two analyses. In this case it is possible to observe that the h(bb̄) + ET miss analysis presents a maximum in sensitivity around the maximal mixing condition. The h(γγ) + ET miss analysis instead shows a local sensitivity minimum around sin θ ∼ 0.55. Finally, figure 21 presents the reach of the various experimental searches in a cosmolog- ical perspective, following the prescription of the fourth benchmark scenario. In this case, the observed exclusion limits in terms of the ratio of the excluded cross-section to the nom- inal cross-section of the model are investigated as a function of the DM mass, which is the parameter with the strongest impact on the relic density predicted by the 2HDM+a model. The region beyond mχ = 200 GeV was not explored by the h(bb̄) + ET miss analysis, thus the exclusion is not shown. For the same reason, the bb̄ +ET miss exclusion is not shown beyond mχ = 125 GeV. The long-dashed line indicates the computed relic density for the 2HDM+a – 42 – model as a function of the DM mass. The two valleys at mχ = 125 GeV and mχ = 300 GeV determine the two a-funnel and A-funnel regions [78, 209, 210] where the predicted relic density is depleted by the resonant enhancement of the processes χχ̄ → A/a → SM. The plateau around and above mχ ∼ 200 GeV is determined by the increase in annihilation cross-section of the DM particles close to threshold for χχ̄ → ha → SM and χχ̄ → tt̄. For DM masses around ma /2 or mχ > 170 GeV the model predicts a relic density which is equal to or below the thermal value, Ωh2 = 0.12. As the DM mass increases further, annihilation via single s-channel diagrams is more and more suppressed and the observed DM relic den- sity can again be reproduced. At low values of ma this happens around mχ ∼ 10 TeV and is outside the range in figure 21. For all X + ET miss signatures considered, the sensitivity JHEP05(2019)142 is independent of the DM mass as long as the lightest pseudo-scalar mediator, whose mass is fixed at 250 GeV in this scenario, is allowed to decay into a χχ̄ pair. The Z(``) + ET miss analysis excludes this parameter space. For higher DM masses, the sensitivity of all anal- yses quickly decreases and no exclusion is observed. For mχ > ma /2 all parameter choices that fulfil or deplete the relic density value are still unconstrained. 6.4 Scalar dark energy model The results of the jet+ET miss and tt̄ +E miss analyses are interpreted in terms of limits on T the two Lagrangian effective operators L1 and L2 for a scalar DE model, introduced in section 2.4. The results are derived as a function of the suppression scale, M1 and M2 , for each operator and the effective coupling associated with the UV completion of the EFT, g∗ , and are shown in figure 22. The EFT operators are only valid in the regime where the momentum transfer is Qtr  M . For the limits shown in figure 22, it is assumed that the EFT approximation is valid for events where Qtr < g∗ M . For events failing this requirement, the iterative rescaling procedure detailed in ref. [75] is applied. The tt̄ +ET miss analysis yields the most stringent constraints on the L1 operator (figure 22a), as expected from the fact that the interaction described by L1 is proportional to the masses of the SM fermions to which the DE scalar couples. The limits are obtained from the search channel (fully hadronic, semileptonic or fully leptonic top pair decays) that provides the smallest expected CLs value. The fully-hadronic and semileptonic channels contribute the most and similarly to the final sensitivity of the analysis, which excludes a suppression scale of about 200 GeV for g∗ & π 2 . The tt̄ +ET miss search is not yet sensitive to weakly coupled models, due to the high momentum transfers involved in the production of the top quarks, which are close to the exclusion limit. The jet+ET miss analysis yields the most stringent constraints on the L operator (fig- 2 ure 22b), due to the fact that this interaction is proportional to the momenta of the particles involved, excluding up to M ' 1.2 TeV for g∗ & π. Due to the absence of heavy particles in the final state, the region of EFT validity for the jet+ET miss search is larger, with the constraints extending to lower values of the effective coupling. These results improve upon the constraints on the disformal operator from astrophys- ical probes and non-collider experiments by several orders of magnitude [211] and also represent a significant improvement on the limits obtained by a similar reinterpretation of √ ATLAS and CMS results that made use of a smaller dataset at s = 8 TeV [82]. – 43 – 1600 M1 [GeV] M2 [GeV] 350 ATLAS s = 13 TeV, 36.1 fb -1 1400 300 miss L1 operator, tt+ET 1200 250 Limits at 95% CL PDF,scale Observed (± 1σtheory ) 1000 ATLAS Expected (CLs) -1 200 s = 13 TeV, 36.1 fb Expected ± 1σ 800 L2 operator, jet+E miss Expected ± 2σ T 150 Limits at 95% CL Excluded 600 PDF,scale Observed (± 1σtheory ) 100 400 Expected (CLs) Expected ± 1σ 50 200 Expected ± 2σ Excluded 0 0 5 6 7 8 9 10 11 12 0 2 4 6 8 10 12 JHEP05(2019)142 g g * * (a) (b) Figure 22. Exclusion plots for (a) L1 and (b) L2 on the (g∗ , M ) plane, after rescaling to take into account the EFT validity criterion [75]. 7 Conclusions This paper summarises the lively experimental programme of searches for mediator-based particle dark matter and scalar dark energy performed by the ATLAS Collaboration. The analyses presented are based on up to 37 fb−1 of proton-proton collisions data at a centre-of- √ mass energy of s = 13 TeV collected by the ATLAS detector at the LHC in 2015 and 2016. √ The h(inv) analysis considers up to 4.7 fb−1 at centre-of-mass energy of s = 7 TeV and √ 20.3 fb−1 at centre-of-mass energy of s = 8 TeV. The results from the searches presented are in agreement with the Standard Model predictions, thus results are translated into exclusion limits on mediator-based dark matter and dark energy models. Results on simplified models with the exchange of a vector or axial-vector mediator in the s-channel with Dirac fermions as dark matter candidates are compared across different visible and invisible final states. In particular, additional interpretations for these models are presented for Z(``) + ET miss , W/Z(qq 0 ) + E miss and all resonance searches except for T boosted dijet + ISR. Masses of leptophobic (leptophilic) vector and axial-vector mediators between 200 GeV and 2.5 TeV (3.5 TeV), for coupling values gq = 0.25 and gχ = 1, and mχ = 1 TeV, are excluded at 95% CL. Results from h(bb̄) + ET miss and h(γγ) + E miss final T states are compared in this paper in the context of a baryon-charged interaction; masses of the ZB0 boson are excluded up to 1.9 TeV for m = 1 GeV and coupling values of g = 1 χ χ and gq = 1/3. Strong limits on a flavour-changing mediator model are set thank to two complementary search approaches targeting visible and invisible decays of the mediator, 0 ZVFC . Masses up to 1.85 TeV for coupling values of gq = 0.35 and gχ = 1.0 are excluded for invisible decays, while gq coupling values between 0.14 and 0.35 for mediator masses between 1 TeV and 3 TeV are excluded for visible decays. Exclusion limits for simplified model of dark matter production including a colour- neutral scalar (pseudo-scalar) mediator are compared for tt̄ +ET miss , bb̄ +E miss and T jet+ET miss final states. Mediator masses below 45 GeV (in the range 15–25 GeV) are ex- cluded for dark matter particles with mχ = 1 GeV and gχ = 1. Masses for colour-charged – 44 – mediators, coupling to first- and second-generation left-handed quarks, are excluded up to 1.7 TeV, for mχ = 50 GeV for gχ = 1. Colour-charged mediators that couple to right- handed b-quarks (t-quarks) are excluded for masses up to 1.4 TeV (3.4 TeV) for low dark matter masses. A first interpretation of an extended two-Higgs-doublet model with an additional pseudo-scalar, a, which couples the dark matter particles to the Standard Model is used to study the broad phenomenology with diverse final-state signatures predicted by this type of model. Masses of the pseudo-scalar mediator, a, are excluded up to 350 GeV for mA = mH = mH ± = 1 TeV, sin θ = 0.35 and tan β = 1.0. The Z(``) + ET miss and h(bb̄) + ETmiss searches are the most sensitive analyses in this high mediator-mass region. JHEP05(2019)142 Previously published limits on a two-Higgs-doublet model with an additional vector medi- ator are improved upon by the statistical combination of the two decay channels studied: h(bb̄) + ETmiss and h(γγ) + E miss . Mediator masses between 400 GeV and 2.5 TeV are T excluded for dark matter masses of 100 GeV. Finally, a Horndeski model for dark energy is studied in the context of ATLAS searches. This model introduces a dark energy scalar which couples to gravity. Limits on the two miss and jet+E miss analyses, Lagrangian effective operators, L1 and L2 , are set by the tt̄ +ET T respectively. The suppression scale is excluded up to 200 GeV for g∗ = π 2 for the L1 operator. For the L2 operator, suppression scales up to 1.2 TeV for g∗ = π are excluded. These results are the first interpretation of a dark energy model by a collider experiment. In this paper, many interpretations in the context of DM and DE models were added with respect to previous publications. This allowed to restrict very significantly the avail- able parameter space of spin-0, spin-1 and 2HDM-based mediator-DM models as well as EFT DE models. Acknowledgments We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Aus- tralia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, CRC and Compute Canada, Canada; – 45 – COST, ERC, ERDF, Horizon 2020, and Marie Sklodowska-Curie Actions, European Union; Investissements d’ Avenir Labex and Idex, ANR, France; DFG and AvH Foundation, Ger- many; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF, Israel; CERCA Programme Generalitat de Catalunya, Spain; The Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (U.K.) and BNL (U.S.A.), the Tier-2 facilities worldwide and large non-WLCG resource providers. Ma- JHEP05(2019)142 jor contributors of computing resources are listed in ref. [233]. A Signal models generation details The model implementations, settings and parameter scans used in this paper follow the prescriptions of the DM Forum/LHC DM Working Group [75–78]. and all generation settings used for signal models in this paper are summarised in tables 4, 5 and 6. A.1 V/AV models For all V/AV models, reconstructed samples were produced only for a specific reference scenario (either a vector or an axial-vector leptophobic mediator model). Rescaling factors for the acceptance (wA ) and the cross-section (wσ ) were calculated to match the acceptance and cross-section of each of the other scenarios to the reference. The acceptance weights were calculated for each (mZ 0 , mχ ) mass hypothesis as the ratio of the particle-level ac- ceptance for each of the NLO benchmark models considered (ANLO truth ) to the particle-level acceptance of the analysis for the reference NLO scenario in a fiducial region (Aref truth ): ANLO truth (mZ 0 , mχ ) wA (mZ 0 , mχ ) = . Aref truth (mZ 0 , mχ ) The cross-section weights were calculated for each (mZ 0 , mχ ) mass hypothesis in a similar way, as the ratio of the reference cross-section at NLO to each cross-section of the four NLO benchmark models. The acceptance rescaling weights were found to be consistent with unity for the Z 0 (χχ̄) + j and Z 0 (χχ̄) + γ signatures. A few specific exceptions apply to this treatment. In case of the Z 0 (χχ̄) + j signature, the cross-section rescaling factors were calculated from LO samples (DMSimp [116, 212] generated with MG5 aMC@NLO 2.4.3 (LO) [213]) and applied to the samples described in table 4. In the specific case of the Z 0 (χχ̄)+V signature, the baseline samples were generated at LO and rescaled at particle level to match the NLO samples described in the table. Finally, the exclusions from the resonance searches (dijet, dilepton, dibjet) as a function of the (mZ 0 , mχ ) interpretations are derived from the limits calculated for Gaussian-shape resonances [214], and the samples in table 4 are only used to derive the cross-section normalisation for the final results and the limits for the leptophobic ZA 0 mediator models as a function of the universal coupling strength. The Z 0 (tt̄) samples were obtained from – 46 – Cross- Model and Final State UFO Generator and Parton Shower Additional details section Particle-level rescaling of lepto- Z 0 (χχ̄) + j DMV [26, 215] powheg-box v2 [216] + Pythia 8.205 [217] NLO phobic ZA 0 scenario of ref. [26] (see appendix A.1) 0 Leptophobic ZA scenario simu- 0 MG5 aMC@NLO 2.4.3 (NLO) [213] + Pythia lated, other scenarios obtained Z (χχ̄) + γ DMSimp [116, 218] NLO 8.212 by cross-section rescaling (see appendix A.1) Particle-level rescaling of LO 0 samples of ref. [20] to each of Z (χχ̄) + V DMSimp MG5 aMC@NLO 2.5.3 (NLO) + Pythia 8.212 NLO the four NLO scenarios (see ap- pendix A.1) 0 Leptophobic ZA scenario simu- lated, other scenario obtained JHEP05(2019)142 0 0 Z (qq) or Z (qq)+ISR DMSimp MG5 aMC@NLO 2.2.3 (NLO) + Pythia 8.210 NLO by Gaussian resonance limits and cross-section rescaling [214] 0 Leptophobic ZA scenario simu- 0 lated, other scenario obtained Z (bb̄) DMSimp MG5 aMC@NLO 2.2.3 (NLO) + Pythia 8.210 NLO by Gaussian resonance limits and cross-section rescaling [214] Gaussian resonance limits and Z 0 (``) DMSimp MG5 aMC@NLO 2.2.3 (NLO) NLO cross-section rescaling [214] Particle-level rescaling of the topcolour-assisted technicolour Z 0 (tt̄) DMSimp MG5 aMC@NLO 2.4.3 (LO) + Pythia 8.186 LO samples of ref. [200] (see ap- pendix A.1) 0 0 ZVFC (χχ̄)/ZVFC (ūt) MonotopDMF [219] MG5 aMC@NLO 2.2.3 (LO) +Pythia 8.210 LO Ref. [30] and appendix A.2 Higgs scalar [106, Ref. [22], simulated for h(bb̄) + ZB0 (χχ̄) + h MG5 aMC@NLO 2.2.3 (LO) +Pythia 8.186 LO miss 220] ET 0 2HDM+ZV Zp2HDM [158, 221] MG5 aMC@NLO 2.2.3 (LO) +Pythia 8.186 LO Refs. [22, 23] Table 4. Details of the generation setup and Universal FeynRules Output (UFO) model used for the spin-1 mediator simplified models, for each signature considered in this paper. the topcolour-assisted technicolour samples of [200] rescaled at particle level to match the DMSimp models described in table 4. The correction weights between the two samples were calculated from the bin-by-bin ratio of the invariant mass distributions of the tt̄ system for the two samples at particle level. An additional uncertainty is assigned to account for this procedure as described in section 5. A.2 VFC model The VFC model is studied in two final states: pp → tZVFC 0 → tχχ̄ and pp → tt(j) (via 0 ZVFC ). A complete set of models with the full ATLAS detector simulation was generated as 0 a function of m(ZVFC ) and assuming minimal width and unitary couplings, following the generation settings summarised in table 4. In order to assess the experimental constraints on all the model parameters, gut , gχ and subsequently Γ(ZVFC 0 ), a rescaling procedure is applied. In the case of the tχχ̄ final state, for each point in the parameter space, rescaling factors were calculated at particle level to match the acceptance and cross-section to those of the simulated reference model. Three different matrix-element amplitudes contribute to the same-sign top-quark sig- nature (tt(j)) relevant for this model: (i) prompt tt production in figure 2c, (ii) on-shell – 47 – Cross- Model and Final State UFO Generator and Parton Shower Additional details section a(χχ̄) + j DMS tloop [113, 222] powheg-box v2 + Pythia 8.205 NLO Ref. [26] DMScalarMed loop Up to one additional parton. φ(χχ̄) + tt̄ MG5 aMC@NLO 2.3.3 (LO) + Pythia 8.186 NLO [116] [113, 223] Ref. [25] Up to one additional parton. φ(χχ̄) + bb̄ DMScalarMed loop MG5 aMC@NLO 2.3.3 (LO) + Pythia 8.186 NLO [212] Ref. [25] ηq dmS T [101, 224] MG5 aMC@NLO 2.3.3 (LO) + Pythia 8.186 LO Refs. [26, 101] DM Bflavored ηb MG5 aMC@NLO 2.3.3 (LO) + Pythia 8.186 LO Ref. [25] [131, 225] MonotopDMF ηt MG5 aMC@NLO 2.3.3 (LO) +Pythia 8.210 LO Ref. [30] [30, 219] Cross-section based rescaling Pseudoscalar 2HDM 2HDM+a: χχ̄ + tt̄/bb̄ MG5 aMC@NLO 2.3.3 (LO) NLO from simplified model samples JHEP05(2019)142 [152, 226] of ref. [25] Only gluon-initiated production 2HDM+a: χχ̄ + Z Pseudoscalar 2HDM MG5 aMC@NLO 2.4.3 (LO) + Pythia 8.212 LO considered [152] b-quark-initiated production 2HDM+a: χχ̄ + h Pseudoscalar 2HDM MG5 aMC@NLO 2.4.3 (LO) + Pythia 8.212 LO considered only for tan β ≥ 10 2HDM+a: 4t Pseudoscalar 2HDM MG5 aMC@NLO 2.4.3 (LO) + Pythia 8.212 LO Ref. [152] Table 5. Details of the generation setup and Universal FeynRules Output (UFO) model used for the spin-0 mediator models, for each signature considered in this paper. Model UFO Generator and Parton Shower Cross-section Dark Energy Standard Model cosmo no c10 [82] MG5 aMC@NLO 2.6.1 (LO) + Pythia 8.212 LO Table 6. Details of the generation setup and Universal FeynRules Output (UFO) model used for the dark energy model. mediator in figure 2b, (iii) off-shell mediator in figure 2d. The relative contributions of the three amplitudes depend on the model parameters, but not the kinematic properties of each process. The three subprocesses, which were generated separately with full detector simulation, are combined according to the following formula to model the signal kinematics for any choice of parameter values (ξ): ref ref ref dσ(ξ) = α(ξ) dσtt + β(ξ) dσOnShell + γ(ξ) dσOffShell . The functions α, β, γ can be computed with MadGraph as the ratio of the desired cross- section to the baseline cross-section: σtt (ξ) σOnShell (ξ) σOffShell (ξ) α(ξ) ≡ , β(ξ) ≡ , and γ(ξ) ≡ . σtt (ξ ref ) σOnShell (ξ ref ) σOffShell (ξ ref ) A.3 2HDM + a models with heavy-flavour final states The χχ̄ + tt̄/bb̄ signature of the 2HDM+a model can be successfully described [78] as the superposition of the associated production of two heavy-flavour quarks with either the light or the heavy pseudo-scalar mediator, which subsequently decays into a χχ̄ pair. When the masses of the two pseudo-scalar mediators are sufficiently different, the contributions of the two processes can be factorised, and the 2HDM+a model can be described in terms of two sets of colour-neutral pseudo-scalar simplified models, each corresponding to the desired choice for ma and mA . – 48 – The acceptance A of the analysis for each point of interest in the 2HDM+a parameter space is therefore derived as: σa × Asimp (ma ) + σA × Asimp (mA ) A2HDM (mA , ma ) = , σa + σA where Asimp is the acceptance of the analysis for the colour-neutral pseudo-scalar simplified model for a certain mass choice of the A(a)-boson, and σa computed in fully reconstructed samples and σA are the production cross-sections for pp → tt̄a(→ χχ̄) and pp → tt̄A(→ χχ̄), respectively.5 This rescaling is valid in the on-shell region, ma (mA ) > 2mχ [78]. JHEP05(2019)142 B Comparison with direct and indirect searches Searches for weakly-interactive massive particles (WIMPs) [57] represent the current paradigm for searches for particle dark matter (DM). Within this paradigm, understanding the nature of DM requires a measurement of its interaction cross-section with Standard Model particles. This can be achieved using three complementary methods [227], schemat- ically depicted in figure 23 and briefly outlined in the following. Direct searches. These searches aim to measure the elastic scattering of DM with nuclei in low background underground detectors such as CRESST-III [6], LUX [7], PICO [8], DEAP [9], PandaX [10], XENON [11, 12] and SuperCDMS [13, 14]. These direct detection experiments ultimately measure the strength of the interactions between WIMPs and the partons composing protons and neutrons and are sensitive to the properties of the DM halo around Earth. Indirect searches. These searches aim to measure the annihilations or decays of DM particles in astrophysical systems, by means of neutrino detectors such as Su- perKamiokande [15] or IceCube [16] or by means of either ground or space telescopes, for example the H.E.S.S. Cherenkov telescope [17, 18], AMS [228] and Fermi-LAT [19]. This measurement closely relates to the processes that determine the abundance of DM in the early universe and the interpretation of the results depends on the DM distribution in the universe as well as the SM particles into which the DM preferentially annihilates or decays. Collider searches. These searches aim to discover DM particles and to measure the DM production cross-section through collisions of high-energy particles. The most stringent results to date on WIMPs are provided by the ATLAS [20–30], CMS [31, 32, 34, 35, 229] and LHCb [230, 231] experiments at the LHC. Sub-GeV DM candidates are also constrained by the MiniBooNE experiment at Fermilab [232]. The interpretation of these results closely depends on the underlying mechanisms that couple DM to SM particles. In the simplified model framework considered in this paper this underlying mechanism is assumed to be the production of new mediator(s) state(s) which subsequently decay into DM. 5 The procedure is also valid for pp → bb̄a/A production. However the impact of the correction was found to be minimal [78] and is neglected in this paper. – 49 – Collider f 𝜒 Direct f 𝜒 Indirect JHEP05(2019)142 Figure 23. Schematic summary of the complementary approaches used in searches for WIMP DM. The present understanding of the DM puzzle is encompassed in the summary and comparison of the experimental results of these three approaches. Likewise, the discovery of DM as an elementary particle will require determination of its interaction cross-section with SM particles via each of these methods. It is convenient and customary to compare these different approaches in terms of spin-dependent (spin-independent) χ-nucleon scattering cross-sections as a function of the DM mass. In this paper, the ATLAS exclusion limits are converted into bounds on the χ-nucleon scattering cross-sections for the following models: • Vector and axial-vector neutral (V/AV) mediator models (two of the benchmark coupling scenarios, see section 6.1.1 for details). • Vector baryon-charged (VBC) mediator model. • Scalar colour-neutral mediator model. For each model, the translation procedure to convert and compare these limits is well defined and described in ref. [76]. The interpretation in the spin-dependent (SD) and spin-independent (SI) DM-nucleon cross-sections, σSD and σSI , respectively, depends on the mediator mass and the couplings assumptions. Each comparison is valid solely in the context of the specific model and coupling assumptions. The ATLAS limits are always shown at 95% confidence level (CL) and the direct detection limits at 90% CL. ATLAS exclusion limits for pseudo-scalar colour-neutral mediator models should be compared with indirect search experiments in terms of the DM annihilation cross-section hσvrel i, as the rate in direct searches experiments is suppressed by additional velocity- dependent terms entering the cross-section. However, the observed exclusion limits for pseudo-scalar mediator models with a unitary coupling assumption are limited to a very narrow mass range, due to a small data excess in the analysis (figure 17b). Therefore, this comparison is deferred to the results with the full Run-2 dataset. The observed limits for the V/AV, VBC and scalar mediator models are compared with limits from direct search experiments in figures 24–26. The excluded regions are indicated by shaded areas inside the contours. Each combined contour summarises the ATLAS results for each considered model, obtained by using the best expected limit for – 50 – each parameter point in the figure. When the contour does not close inside the plotted area, the exclusion of smaller scattering cross-sections does not imply that larger scattering cross-sections (beyond the vertical axis range) are also excluded. The spin-dependent WIMP-neutron (WIMP-proton) scattering cross-section in the context of the leptophobic ZA 0 mediator model is shown in the upper (lower) panel of figure 24. The difference between the WIMP-proton and WIMP-neutron cross-sections is negligible. The ATLAS exclusion curves are therefore identical in the two panels. The collider searches for this specific leptophobic axial-vector model complement the reach of the direct searches and extend beyond it, being particularly sensitive in the low-DM-mass parameter space, where the LUX and PICO experiments have less sensitivity due to the JHEP05(2019)142 very low-energy recoils that such low-mass dark matter particles would induce. As in the case of the interpretation of the results in terms of mediator and DM masses (section 6.1.1), if the values chosen for the couplings are reduced, the relative interplay between direct and collider searches changes. This is exemplified by the change of lepton and quark couplings in the leptophilic ZA 0 mediator model shown in figure 25, where the reach of resonant dijet final states is greatly reduced in favour of dilepton searches (differently for the two scenarios) and limited to mediator masses above 200 GeV. The sensitivity of the ET miss + X searches is the same for the two models in figures 24 and 25b. This is a coincidental result of two opposite effects [76]: the fact that the scattering cross-section limit is inversely proportional to the mediator mass reach (raised to the fourth power), which is higher in the leptophobic mediator model (figure 12a), and the fact that the σSD limit is proportional to gq2 , which is lower in the leptophilic mediator model. The spin-independent WIMP-nucleon scattering cross-section results for leptophobic, leptophilic, or baryon-charged vector mediator Z 0 and scalar colour-neutral mediator φ are compared with the most stringent direct detection limits to date from the LUX, CRESST- II, XENON1T, SuperCDMS and PandaX experiments in figure 26. One contour for each model is presented in the figure and it includes the combination, based on the best expected limit for each parameter point, of every analysis considered for each model and presented in section 6. The excluded regions are indicated by shaded areas inside the contour. As before, when the contour does not close inside the plotted area, the exclusion of smaller scattering cross-sections does not imply that larger scattering cross-sections (beyond the vertical axis range) are also excluded. The collider searches in this case complement the reach of the di- rect searches for mχ . 5 GeV. By comparing the exclusion reach of the ATLAS searches for each of the four models considered in figure 26, it is possible to gauge the importance of the production mechanism assumptions for the collider limits, which represent a complemen- tary and not exclusive approach to DM searches with respect to direct and indirect searches. – 51 – − 37 10 σSD (χ-neutron) [cm2] Dijet Dijet s = 13 TeV, 37.0 fb-1 10 − 38 ATLAS PRD 96, 052004 (2017) Dijet TLA s = 13 TeV, 29.3 fb-1 LUX PRL 121 (2018) 0818016 Dijet + ISR s = 13 TeV, 15.5 fb-1 − 39 10 ATLAS-CONF-2016-070 (Preliminary) tt resonance − 40 s = 13 TeV, 36.1 fb-1 10 EPJC 78 (2018) 565 tt resonance Dibjet 10−41 miss s = 13 TeV, 36.1 fb-1 ET +X PRD 98 (2018) 032016 Dibjet 10−42 Emiss T +X miss -1 ET +γ s = 13 TeV, 36.1 fb 10 − 43 Dijet Eur. Phys. J. C 77 (2017) 393 miss E T +jet s = 13 TeV, 36.1 fb-1 JHEP05(2019)142 JHEP miss 1801 (2018) 126 -1 E T +Z(ll) s = 13 TeV, 36.1 fb − 44 PLB 776 (2017) 318 10 miss E T +V(had) s = 13 TeV, 36.1 fb-1 JHEP 10 (2018) 180 − 45 Axial-vector mediator, Dirac DM 10 gq = 0.25, g = 0, gχ = 1 LUX l Phys. Rev. Lett. 116, 161302 (2016) ATLAS limits at 95% CL, direct detection limits at 90% CL − 46 10 3 1 10 102 10 mχ [GeV] (a) − 37 10 σSD (χ-proton) [cm2] Dijet Dijet s = 13 TeV, 37.0 fb-1 10 − 38 ATLAS PICO-60 C3F8 PRD 96, 052004 (2017) Dijet TLA s = 13 TeV, 29.3 fb-1 PRL 121 (2018) 0818016 Dijet + ISR s = 13 TeV, 15.5 fb-1 − 39 10 ATLAS-CONF-2016-070 (Preliminary) tt resonance − 40 s = 13 TeV, 36.1 fb-1 10 EPJC 78 (2018) 565 tt resonance Dibjet 10−41 miss s = 13 TeV, 36.1 fb-1 ET +X PRD 98 (2018) 032016 Dibjet 10−42 Emiss T +X miss -1 ET +γ s = 13 TeV, 36.1 fb 10 − 43 Dijet Eur. Phys. J. C 77 (2017) 393 miss E T +jet s = 13 TeV, 36.1 fb-1 JHEP miss 1801 (2018) 126 -1 E T +Z(ll) s = 13 TeV, 36.1 fb 10−44 PLB 776 (2017) 318 miss E T +V(had) s = 13 TeV, 36.1 fb-1 JHEP 10 (2018) 180 − 45 Axial-vector mediator, Dirac DM 10 gq = 0.25, g = 0, gχ = 1 PICO-60 C3F8 l PRL 118, 251301 (2017) ATLAS limits at 95% CL, direct detection limits at 90% CL − 46 10 3 1 10 102 10 mχ [GeV] (b) Figure 24. A comparison of the inferred limits with the constraints from direct detection ex- periments on (a) the spin-dependent WIMP-neutron or (b) WIMP-proton scattering cross-section in the context of the Z 0 -like simplified model with axial-vector couplings. The results from this analysis, excluding the region to the left of the contour, are compared with limits from direct de- tection experiments. LHC limits are shown at 95% CL and direct detection limits at 90% CL. The comparison is valid solely in the context of this model, assuming a mediator width fixed by the dark matter mass and coupling values gq = 0.1, g` = 0.1, and gχ = 1. LHC searches and direct detection experiments exclude the shaded areas. Exclusions of smaller scattering cross-sections do not imply miss that larger scattering cross-sections are also excluded. The resonance and ET +X exclusion region represents the union of exclusions from all analyses of that type. – 52 – − 37 10 σSI (χ-nucleon) [cm2] Dilepton s = 13 TeV, 36.1 fb-1 − 38 10 ATLAS JHEP 10 (2017) 182 Dilepton − 39 Dijet 10 Dijet s = 13 TeV, 37.0 fb-1 PRD 96, 052004 (2017) − 40 Dijet TLA s = 13 TeV, 29.3 fb-1 10 CRESST III Dijet PRL 121 (2018) 0818016 Emiss T +X 10−41 Emiss T +X E miss T +γ s = 13 TeV, 36.1 fb-1 − 42 Eur. Phys. J. C 77 (2017) 393 10 DarkSide-50 miss E T +jet s = 13 TeV, 36.1 fb-1 JHEP 1801 (2018) 126 − 43 10 CRESST III arXiv:1904.00498 − 44 10 XENON1T aX LUX PRL 121, 111302 (2018) JHEP05(2019)142 − 45 Pand 10 PandaX N1T XENO PRL 117, 121303 (2016) − 46 10 DarkSide-50 Vector mediator, Dirac DM PRL 121, 081307 (2018) − 47 10 gq = 0.1, g = 0.01, gχ = 1 l LUX ATLAS limits at 95% CL, direct detection limits at 90% CL PRL 118, 021303 (2017) − 48 10 2 3 1 10 10 10 mχ [GeV] (a) − 37 10 σSD (χ-neutron) [cm2] Dilepton s = 13 TeV, 36.1 fb-1 JHEP 10 (2017) 182 10 − 38 ATLAS LUX Dijet − 39 Dijet s = 13 TeV, 37.0 fb-1 10 PRD 96, 052004 (2017) Dijet TLA s = 13 TeV, 29.3 fb-1 PRL 121 (2018) 0818016 − 40 10 Emiss T +X E miss T +γ s = 13 TeV, 36.1 fb-1 10−41 Eur. Phys. J. C 77 (2017) 393 miss E T +jet s = 13 TeV, 36.1 fb-1 JHEP 1801 (2018) 126 10−42 Emiss Dijet LUX T +X Phys. Rev. Lett. 116, 161302 (2016) − 43 10 10−44 Dilepton − 45 Axial-vector mediator, Dirac DM 10 gq = 0.1, g = 0.1, gχ = 1 l ATLAS limits at 95% CL, direct detection limits at 90% CL − 46 10 3 1 10 102 10 mχ [GeV] (b) Figure 25. A comparison of the inferred limits with the constraints from direct detection exper- iments on the spin-independent WIMP-nucleon (spin-dependent WIMP-neutron) scattering cross- section in the context of (a) the Z 0 -like simplified model with leptophilic vector or (b) axial-vector couplings. The results from this analysis, excluding the region to the left of the contour, are com- pared with limits from the direct detection experiments. LHC limits are shown at 95% CL and direct detection limits at 90% CL. The comparison is valid solely in the context of this model, assuming a mediator width fixed by the dark matter mass and the coupling values highlighted in each figure. LHC searches and direct detection experiments exclude the shaded areas. Exclusions of smaller scat- tering cross-sections do not imply that larger scattering cross-sections are also excluded. The reso- miss nance and ET +X exclusion region represents the union of exclusions from all analyses of that type. – 53 – σSI (χ-nucleon) [cm2] ATLAS Vector Z' Vector mediator, Dirac DM 10−39 gq = 0.25, g = 0, gχ = 1 l Phys. Rev. D 96 (2017) 052004 Phys. Rev. Lett. 121 (2018) 081801 −40 10 C Preliminary ATLAS-CONF-2016-070 R ES Phys. Rev. D 98 (2018) 032016 lar ST S Sca Eur. Phys. J. C 78 (2018) 565 ATLA III ATLAS Z' baryonic Eur. Phys. J. C 77 (2017) 393 10−41 JHEP 01 (2018) 126 PLB 776 (2017) 318 JHEP 10 (2018) 180 ATLAS Vector Z' 10−42 DarkS ATLAS Z' baryonic ide-50 Z' baryonic, Dirac DM sinθ = 0.3, gq = 1/3, gχ = 1 −43 10 Phys. Rev. Lett. 119 (2017) 181804 Phys. Rev. D 96 (2017) 112004 ATLAS Scalar JHEP05(2019)142 10−44 Scalar mediator, Dirac DM gq = 1, gχ = 1 aX LUX Pand Eur. Phys. J. C 78 (2018) 18 10−45 DarkSide-50 Phys. Rev. Lett. 121 (2018) 081307 N1T CRESST III 10−46 XENO arXiv:1904.00498 ATLAS ATLAS limits at 95% CL, XENON1T -1 Phys. Rev. Lett. 121 (2018) 111302 s = 13 TeV, 29.3-37.0 fb direct detection limits at 90% CL 10−47 2 3 PandaX 1 10 10 10 Phys. Rev. Lett. 117 (2016) 121303 LUX mχ [GeV] Phys. Rev. Lett. 118 (2017) 021303 Figure 26. A comparison of the inferred limits with the constraints from direct detection experiments on the spin-independent WIMP-nucleon scattering cross-section. The results from ATLAS analyses, excluding the shaded regions, are compared with limits from direct detection experiments. LHC limits are shown at 95% CL and direct detection limits at 90% CL. The comparison is valid solely in the context of this model, assuming a mediator width fixed by the dark matter mass and coupling values gq = 0.25, g` = 0 or gq = 0.1, g` = 0.01 for the neutral-mediator model and coupling gq = 0.33 for the baryon-charged mediator. 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Fullana Torregrosa174 , E. Fumagalli55b,55a , T. Fusayasu116 , J. Fuster174 , A. Gabrielli23b,23a , A. Gabrielli18 , G.P. Gach83a , S. Gadatsch54 , P. Gadow115 , G. Gagliardi55b,55a , L.G. Gagnon109 , C. Galea27b , B. Galhardo140a,140c , E.J. Gallas135 , B.J. Gallop144 , P. Gallus142 , G. Galster40 , R. Gamboa Goni92 , K.K. Gan126 , S. Ganguly180 , J. Gao60a , Y. Gao90 , Y.S. Gao31,m , C. Garcı́a174 , J.E. Garcı́a Navarro174 , J.A. Garcı́a Pascual15a , C. Garcia-Argos52 , M. Garcia-Sciveres18 , R.W. Gardner37 , N. Garelli153 , S. Gargiulo52 , V. Garonne134 , JHEP05(2019)142 A. Gaudiello55b,55a , G. Gaudio70a , I.L. Gavrilenko110 , A. Gavrilyuk111 , C. Gay175 , G. Gaycken24 , E.N. Gazis10 , C.N.P. Gee144 , J. Geisen53 , M. Geisen99 , M.P. Geisler61a , C. Gemme55b , M.H. Genest58 , C. Geng105 , S. Gentile72a,72b , S. George93 , T. Geralis44 , D. Gerbaudo14 , G. Gessner47 , S. Ghasemi151 , M. Ghasemi Bostanabad176 , M. Ghneimat24 , A. Ghosh77 , B. Giacobbe23b , S. Giagu72a,72b , N. 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Grabowska-Bold83a , P.O.J. Gradin172 , E.C. Graham90 , J. Gramling171 , E. Gramstad134 , S. Grancagnolo19 , M. Grandi156 , V. Gratchev138 , P.M. Gravila27f , F.G. Gravili67a,67b , C. Gray57 , H.M. Gray18 , C. Grefe24 , K. Gregersen96 , I.M. Gregor46 , P. Grenier153 , K. Grevtsov46 , N.A. Grieser128 , J. Griffiths8 , A.A. Grillo146 , K. Grimm31,l , S. Grinstein14,y , J.-F. Grivaz132 , S. Groh99 , E. Gross180 , J. Grosse-Knetter53 , Z.J. Grout94 , C. Grud105 , A. Grummer118 , L. Guan105 , W. Guan181 , J. Guenther36 , A. Guerguichon132 , F. Guescini168a , D. Guest171 , R. Gugel52 , B. Gui126 , T. Guillemin5 , S. Guindon36 , U. Gul57 , J. Guo60c , W. Guo105 , Y. Guo60a,s , Z. Guo101 , R. Gupta46 , S. Gurbuz12c , G. Gustavino128 , P. Gutierrez128 , C. Gutschow94 , C. Guyot145 , M.P. Guzik83a , C. Gwenlan135 , C.B. Gwilliam90 , A. Haas124 , C. Haber18 , H.K. Hadavand8 , N. Haddad35e , A. Hadef60a , S. Hageböck36 , M. Hagihara169 , M. Haleem177 , J. Haley129 , G. Halladjian106 , G.D. Hallewell101 , K. Hamacher182 , P. Hamal130 , K. Hamano176 , H. Hamdaoui35e , G.N. Hamity149 , K. Han60a,ak , L. Han60a , S. Han15a,15d , K. Hanagaki81,v , M. Hance146 , D.M. Handl114 , B. Haney137 , R. Hankache136 , P. Hanke61a , E. Hansen96 , J.B. Hansen40 , J.D. Hansen40 , M.C. Hansen24 , P.H. Hansen40 , E.C. Hanson100 , K. Hara169 , A.S. Hard181 , T. Harenberg182 , S. Harkusha107 , P.F. Harrison178 , N.M. Hartmann114 , Y. Hasegawa150 , A. Hasib50 , S. Hassani145 , S. Haug20 , R. Hauser106 , L. Hauswald48 , L.B. Havener39 , M. Havranek142 , C.M. Hawkes21 , R.J. Hawkings36 , D. Hayden106 , C. Hayes155 , R.L. Hayes175 , C.P. Hays135 , J.M. Hays92 , H.S. Hayward90 , S.J. Haywood144 , F. He60a , M.P. Heath50 , V. Hedberg96 , L. Heelan8 , S. Heer24 , K.K. Heidegger52 , J. Heilman34 , S. Heim46 , T. Heim18 , B. Heinemann46,ar , J.J. Heinrich114 , L. Heinrich124 , C. Heinz56 , J. Hejbal141 , L. Helary61b , A. Held175 , S. Hellesund134 , C.M. Helling146 , S. Hellman45a,45b , C. Helsens36 , R.C.W. Henderson89 , Y. Heng181 , L. Henkelmann61a , S. Henkelmann175 , – 72 – A.M. Henriques Correia36 , G.H. Herbert19 , H. Herde26 , V. Herget177 , Y. Hernández Jiménez33c , H. Herr99 , M.G. Herrmann114 , T. Herrmann48 , G. Herten52 , R. Hertenberger114 , L. Hervas36 , T.C. Herwig137 , G.G. Hesketh94 , N.P. Hessey168a , A. Higashida163 , S. Higashino81 , E. Higón-Rodriguez174 , K. Hildebrand37 , E. Hill176 , J.C. Hill32 , K.K. Hill29 , K.H. Hiller46 , S.J. Hillier21 , M. Hils48 , I. Hinchliffe18 , F. Hinterkeuser24 , M. Hirose133 , D. Hirschbuehl182 , B. Hiti91 , O. Hladik141 , D.R. Hlaluku33c , X. Hoad50 , J. Hobbs155 , N. Hod180 , M.C. Hodgkinson149 , A. Hoecker36 , F. Hoenig114 , D. Hohn52 , D. Hohov132 , T.R. Holmes37 , M. Holzbock114 , L.B.A.H Hommels32 , S. Honda169 , T. Honda81 , T.M. Hong139 , A. Hönle115 , B.H. Hooberman173 , W.H. Hopkins6 , Y. Horii117 , P. Horn48 , A.J. Horton152 , L.A. Horyn37 , J-Y. Hostachy58 , A. Hostiuc148 , S. Hou158 , A. Hoummada35a , J. Howarth100 , J. Hoya88 , M. Hrabovsky130 , J. Hrdinka36 , I. Hristova19 , J. Hrivnac132 , A. Hrynevich108 , T. Hryn’ova5 , JHEP05(2019)142 P.J. Hsu64 , S.-C. Hsu148 , Q. Hu29 , S. Hu60c , Y. Huang15a , Z. Hubacek142 , F. Hubaut101 , M. Huebner24 , F. Huegging24 , T.B. Huffman135 , M. Huhtinen36 , R.F.H. Hunter34 , P. Huo155 , A.M. Hupe34 , N. Huseynov79,af , J. Huston106 , J. Huth59 , R. Hyneman105 , G. Iacobucci54 , G. Iakovidis29 , I. Ibragimov151 , L. Iconomidou-Fayard132 , Z. Idrissi35e , P.I. Iengo36 , R. Ignazzi40 , O. Igonkina120,aa , R. Iguchi163 , T. Iizawa54 , Y. Ikegami81 , M. Ikeno81 , D. Iliadis162 , N. Ilic119 , F. Iltzsche48 , G. Introzzi70a,70b , M. Iodice74a , K. Iordanidou39 , V. Ippolito72a,72b , M.F. Isacson172 , N. Ishijima133 , M. Ishino163 , M. Ishitsuka165 , W. Islam129 , C. Issever135 , S. Istin160 , F. Ito169 , J.M. Iturbe Ponce63a , R. Iuppa75a,75b , A. Ivina180 , H. Iwasaki81 , J.M. Izen43 , V. Izzo69a , P. Jacka141 , P. Jackson1 , R.M. Jacobs24 , V. Jain2 , G. Jäkel182 , K.B. Jakobi99 , K. Jakobs52 , S. Jakobsen76 , T. Jakoubek141 , D.O. Jamin129 , R. Jansky54 , J. Janssen24 , M. Janus53 , P.A. Janus83a , G. Jarlskog96 , N. Javadov79,af , T. Javůrek36 , M. Javurkova52 , F. Jeanneau145 , L. Jeanty131 , J. Jejelava159a,ag , A. Jelinskas178 , P. Jenni52,c , J. Jeong46 , N. Jeong46 , S. Jézéquel5 , H. Ji181 , J. Jia155 , H. Jiang78 , Y. Jiang60a , Z. Jiang153,q , S. Jiggins52 , F.A. Jimenez Morales38 , J. Jimenez Pena174 , S. Jin15c , A. Jinaru27b , O. Jinnouchi165 , H. Jivan33c , P. Johansson149 , K.A. Johns7 , C.A. Johnson65 , K. Jon-And45a,45b , R.W.L. Jones89 , S.D. Jones156 , S. Jones7 , T.J. Jones90 , J. Jongmanns61a , P.M. Jorge140a,140b , J. Jovicevic168a , X. Ju18 , J.J. Junggeburth115 , A. Juste Rozas14,y , A. Kaczmarska84 , M. Kado132 , H. Kagan126 , M. Kagan153 , T. Kaji179 , E. Kajomovitz160 , C.W. Kalderon96 , A. Kaluza99 , A. Kamenshchikov123 , L. Kanjir91 , Y. Kano163 , V.A. Kantserov112 , J. Kanzaki81 , L.S. Kaplan181 , D. Kar33c , M.J. Kareem168b , E. Karentzos10 , S.N. Karpov79 , Z.M. Karpova79 , V. Kartvelishvili89 , A.N. Karyukhin123 , L. Kashif181 , R.D. Kass126 , A. Kastanas45a,45b , Y. Kataoka163 , C. Kato60d,60c , J. Katzy46 , K. Kawade82 , K. Kawagoe87 , T. Kawaguchi117 , T. Kawamoto163 , G. Kawamura53 , E.F. Kay176 , V.F. Kazanin122b,122a , R. Keeler176 , R. Kehoe42 , J.S. Keller34 , E. Kellermann96 , J.J. Kempster21 , J. Kendrick21 , O. Kepka141 , S. Kersten182 , B.P. Kerševan91 , S. Ketabchi Haghighat167 , R.A. Keyes103 , M. Khader173 , F. Khalil-Zada13 , A. Khanov129 , A.G. Kharlamov122b,122a , T. Kharlamova122b,122a , E.E. Khoda175 , A. Khodinov166 , T.J. Khoo54 , E. Khramov79 , J. Khubua159b , S. Kido82 , M. Kiehn54 , C.R. Kilby93 , Y.K. Kim37 , N. Kimura66a,66c , O.M. Kind19 , B.T. King90,∗ , D. Kirchmeier48 , J. Kirk144 , A.E. Kiryunin115 , T. Kishimoto163 , V. Kitali46 , O. Kivernyk5 , E. Kladiva28b,∗ , T. Klapdor-Kleingrothaus52 , M.H. Klein105 , M. Klein90 , U. Klein90 , K. Kleinknecht99 , P. Klimek121 , A. Klimentov29 , T. Klingl24 , T. Klioutchnikova36 , F.F. Klitzner114 , P. Kluit120 , S. Kluth115 , E. Kneringer76 , E.B.F.G. Knoops101 , A. Knue52 , D. Kobayashi87 , T. Kobayashi163 , M. Kobel48 , M. Kocian153 , P. Kodys143 , P.T. Koenig24 , T. Koffas34 , N.M. Köhler115 , T. Koi153 , M. Kolb61b , I. Koletsou5 , T. Kondo81 , N. Kondrashova60c , K. Köneke52 , A.C. König119 , T. Kono125 , R. Konoplich124,an , V. Konstantinides94 , N. Konstantinidis94 , B. Konya96 , R. Kopeliansky65 , S. Koperny83a , K. Korcyl84 , K. Kordas162 , G. Koren161 , A. Korn94 , I. Korolkov14 , E.V. Korolkova149 , N. Korotkova113 , O. Kortner115 , S. Kortner115 , T. Kosek143 , V.V. Kostyukhin24 , A. Kotwal49 , – 73 – A. Koulouris10 , A. Kourkoumeli-Charalampidi70a,70b , C. Kourkoumelis9 , E. Kourlitis149 , V. Kouskoura29 , A.B. Kowalewska84 , R. Kowalewski176 , C. Kozakai163 , W. Kozanecki145 , A.S. Kozhin123 , V.A. Kramarenko113 , G. Kramberger91 , D. Krasnopevtsev60a , M.W. Krasny136 , A. Krasznahorkay36 , D. Krauss115 , J.A. Kremer83a , J. Kretzschmar90 , P. Krieger167 , K. Krizka18 , K. Kroeninger47 , H. Kroha115 , J. Kroll141 , J. Kroll137 , J. Krstic16 , U. Kruchonak79 , H. Krüger24 , N. Krumnack78 , M.C. Kruse49 , T. Kubota104 , S. Kuday4b , J.T. Kuechler46 , S. Kuehn36 , A. Kugel61a , T. Kuhl46 , V. Kukhtin79 , R. Kukla101 , Y. Kulchitsky107,aj , S. Kuleshov147b , Y.P. Kulinich173 , M. Kuna58 , T. Kunigo85 , A. Kupco141 , T. Kupfer47 , O. Kuprash52 , H. Kurashige82 , L.L. Kurchaninov168a , Y.A. Kurochkin107 , A. Kurova112 , M.G. Kurth15a,15d , E.S. Kuwertz36 , M. Kuze165 , J. Kvita130 , T. Kwan103 , A. La Rosa115 , J.L. La Rosa Navarro80d , L. La Rotonda41b,41a , F. La Ruffa41b,41a , C. Lacasta174 , F. Lacava72a,72b , D.P.J. Lack100 , JHEP05(2019)142 H. Lacker19 , D. Lacour136 , E. Ladygin79 , R. Lafaye5 , B. Laforge136 , T. Lagouri33c , S. Lai53 , S. Lammers65 , W. Lampl7 , E. Lançon29 , U. Landgraf52 , M.P.J. Landon92 , M.C. Lanfermann54 , V.S. Lang46 , J.C. Lange53 , R.J. Langenberg36 , A.J. Lankford171 , F. Lanni29 , K. Lantzsch24 , A. Lanza70a , A. Lapertosa55b,55a , S. Laplace136 , J.F. Laporte145 , T. Lari68a , F. Lasagni Manghi23b,23a , M. Lassnig36 , T.S. Lau63a , A. Laudrain132 , A. Laurier34 , M. Lavorgna69a,69b , M. Lazzaroni68a,68b , B. Le104 , O. Le Dortz136 , E. Le Guirriec101 , M. LeBlanc7 , T. LeCompte6 , F. Ledroit-Guillon58 , C.A. Lee29 , G.R. Lee147a , L. Lee59 , S.C. Lee158 , S.J. Lee34 , B. Lefebvre103 , M. Lefebvre176 , F. Legger114 , C. Leggett18 , K. Lehmann152 , N. Lehmann182 , G. Lehmann Miotto36 , W.A. Leight46 , A. Leisos162,w , M.A.L. Leite80d , R. Leitner143 , D. Lellouch180,∗ , K.J.C. Leney42 , T. Lenz24 , B. Lenzi36 , R. Leone7 , S. Leone71a , C. Leonidopoulos50 , A. Leopold136 , G. Lerner156 , C. Leroy109 , R. Les167 , C.G. Lester32 , M. Levchenko138 , J. Levêque5 , D. Levin105 , L.J. Levinson180 , B. Li15b , B. Li105 , C-Q. Li60a,am , H. Li60a , H. Li60b , K. Li153 , L. Li60c , M. Li15a , Q. Li15a,15d , Q.Y. Li60a , S. Li60d,60c , X. Li60c , Y. Li46 , Z. Liang15a , B. Liberti73a , A. Liblong167 , K. Lie63c , S. Liem120 , C.Y. Lin32 , K. Lin106 , T.H. Lin99 , R.A. Linck65 , J.H. Lindon21 , A.L. Lionti54 , E. Lipeles137 , A. Lipniacka17 , M. Lisovyi61b , T.M. Liss173,at , A. Lister175 , A.M. Litke146 , J.D. Little8 , B. Liu78 , B.L Liu6 , H.B. Liu29 , H. Liu105 , J.B. Liu60a , J.K.K. Liu135 , K. Liu136 , M. Liu60a , P. Liu18 , Y. Liu15a,15d , Y.L. Liu60a , Y.W. Liu60a , M. Livan70a,70b , A. Lleres58 , J. Llorente Merino15a , S.L. Lloyd92 , C.Y. Lo63b , F. Lo Sterzo42 , E.M. Lobodzinska46 , P. Loch7 , T. Lohse19 , K. Lohwasser149 , M. Lokajicek141 , J.D. Long173 , R.E. Long89 , L. Longo36 , K.A. Looper126 , J.A. Lopez147b , I. Lopez Paz100 , A. Lopez Solis149 , J. Lorenz114 , N. Lorenzo Martinez5 , M. Losada22 , P.J. Lösel114 , A. Lösle52 , X. Lou46 , X. Lou15a , A. Lounis132 , J. Love6 , P.A. Love89 , J.J. Lozano Bahilo174 , H. Lu63a , M. Lu60a , Y.J. Lu64 , H.J. Lubatti148 , C. Luci72a,72b , A. Lucotte58 , C. Luedtke52 , F. Luehring65 , I. Luise136 , L. Luminari72a , B. Lund-Jensen154 , M.S. Lutz102 , D. Lynn29 , R. Lysak141 , E. Lytken96 , F. Lyu15a , V. Lyubushkin79 , T. Lyubushkina79 , H. Ma29 , L.L. Ma60b , Y. Ma60b , G. Maccarrone51 , A. Macchiolo115 , C.M. Macdonald149 , J. Machado Miguens137,140b , D. Madaffari174 , R. Madar38 , W.F. Mader48 , N. Madysa48 , J. Maeda82 , K. Maekawa163 , S. Maeland17 , T. Maeno29 , M. Maerker48 , A.S. Maevskiy113 , V. Magerl52 , N. Magini78 , D.J. Mahon39 , C. Maidantchik80b , T. Maier114 , A. Maio140a,140b,140d , O. Majersky28a , S. Majewski131 , Y. Makida81 , N. Makovec132 , B. Malaescu136 , Pa. Malecki84 , V.P. Maleev138 , F. Malek58 , U. Mallik77 , D. Malon6 , C. Malone32 , S. Maltezos10 , S. Malyukov36 , J. Mamuzic174 , G. Mancini51 , I. Mandić91 , L. Manhaes de Andrade Filho80a , I.M. Maniatis162 , J. Manjarres Ramos48 , K.H. Mankinen96 , A. Mann114 , A. Manousos76 , B. Mansoulie145 , I. Manthos162 , S. Manzoni120 , A. Marantis162 , G. Marceca30 , L. Marchese135 , G. Marchiori136 , M. Marcisovsky141 , C. Marcon96 , C.A. Marin Tobon36 , M. Marjanovic38 , F. Marroquim80b , Z. Marshall18 , M.U.F Martensson172 , S. Marti-Garcia174 , C.B. Martin126 , T.A. Martin178 , V.J. Martin50 , B. Martin dit Latour17 , – 74 – M. Martinez14,y , V.I. Martinez Outschoorn102 , S. Martin-Haugh144 , V.S. Martoiu27b , A.C. Martyniuk94 , A. Marzin36 , L. Masetti99 , T. Mashimo163 , R. Mashinistov110 , J. Masik100 , A.L. Maslennikov122b,122a , L.H. Mason104 , L. Massa73a,73b , P. Massarotti69a,69b , P. Mastrandrea71a,71b , A. Mastroberardino41b,41a , T. Masubuchi163 , A. Matic114 , P. Mättig24 , J. Maurer27b , B. Maček91 , S.J. Maxfield90 , D.A. Maximov122b,122a , R. Mazini158 , I. Maznas162 , S.M. Mazza146 , S.P. Mc Kee105 , T.G. McCarthy115 , L.I. McClymont94 , W.P. McCormack18 , E.F. McDonald104 , J.A. Mcfayden36 , M.A. McKay42 , K.D. McLean176 , S.J. McMahon144 , P.C. McNamara104 , C.J. McNicol178 , R.A. McPherson176,ad , J.E. Mdhluli33c , Z.A. Meadows102 , S. Meehan148 , T. Megy52 , S. Mehlhase114 , A. Mehta90 , T. Meideck58 , B. Meirose43 , D. Melini174 , B.R. Mellado Garcia33c , J.D. Mellenthin53 , M. Melo28a , F. Meloni46 , A. Melzer24 , S.B. Menary100 , E.D. Mendes Gouveia140a,140e , L. Meng36 , X.T. Meng105 , S. Menke115 , E. Meoni41b,41a , JHEP05(2019)142 S. Mergelmeyer19 , S.A.M. Merkt139 , C. Merlassino20 , P. Mermod54 , L. Merola69a,69b , C. Meroni68a , J.K.R. Meshreki151 , A. Messina72a,72b , J. Metcalfe6 , A.S. Mete171 , C. Meyer65 , J. Meyer160 , J-P. Meyer145 , H. Meyer Zu Theenhausen61a , F. Miano156 , R.P. Middleton144 , L. Mijović50 , G. Mikenberg180 , M. Mikestikova141 , M. Mikuž91 , M. Milesi104 , A. Milic167 , D.A. Millar92 , D.W. Miller37 , A. Milov180 , D.A. Milstead45a,45b , R.A. Mina153,q , A.A. Minaenko123 , M. Miñano Moya174 , I.A. Minashvili159b , A.I. Mincer124 , B. Mindur83a , M. Mineev79 , Y. 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Polini23b , C.S. Pollard46 , V. Polychronakos29 , D. Ponomarenko112 , L. Pontecorvo36 , G.A. Popeneciu27d , D.M. Portillo Quintero136 , S. Pospisil142 , K. Potamianos46 , I.N. Potrap79 , C.J. Potter32 , H. Potti11 , T. Poulsen96 , J. Poveda36 , T.D. Powell149 , M.E. Pozo Astigarraga36 , P. Pralavorio101 , S. Prell78 , D. Price100 , M. Primavera67a , S. Prince103 , M.L. Proffitt148 , N. Proklova112 , K. Prokofiev63c , F. Prokoshin147b , S. Protopopescu29 , J. Proudfoot6 , M. Przybycien83a , A. Puri173 , P. Puzo132 , J. Qian105 , Y. Qin100 , A. Quadt53 , M. Queitsch-Maitland46 , A. Qureshi1 , P. Rados104 , F. Ragusa68a,68b , G. Rahal97 , J.A. Raine54 , S. Rajagopalan29 , A. Ramirez Morales92 , K. Ran15a,15d , T. Rashid132 , S. Raspopov5 , M.G. Ratti68a,68b , D.M. Rauch46 , F. Rauscher114 , S. Rave99 , B. Ravina149 , I. Ravinovich180 , J.H. Rawling100 , M. Raymond36 , A.L. Read134 , N.P. Readioff58 , M. Reale67a,67b , D.M. Rebuzzi70a,70b , A. Redelbach177 , G. Redlinger29 , R.G. 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Talyshev122b,122a , J. Tanaka163 , M. Tanaka165 , R. Tanaka132 , B.B. Tannenwald126 , S. Tapia Araya173 , S. Tapprogge99 , A. Tarek Abouelfadl Mohamed136 , S. Tarem160 , G. Tarna27b,d , G.F. Tartarelli68a , P. Tas143 , M. Tasevsky141 , T. Tashiro85 , E. Tassi41b,41a , A. Tavares Delgado140a,140b , Y. Tayalati35e , JHEP05(2019)142 A.J. Taylor50 , G.N. Taylor104 , P.T.E. Taylor104 , W. Taylor168b , A.S. Tee89 , R. Teixeira De Lima153 , P. Teixeira-Dias93 , H. Ten Kate36 , J.J. Teoh120 , S. Terada81 , K. Terashi163 , J. Terron98 , S. Terzo14 , M. Testa51 , R.J. Teuscher167,ad , S.J. Thais183 , T. Theveneaux-Pelzer46 , F. Thiele40 , D.W. Thomas93 , J.P. Thomas21 , A.S. Thompson57 , P.D. Thompson21 , L.A. Thomsen183 , E. Thomson137 , Y. Tian39 , R.E. Ticse Torres53 , V.O. Tikhomirov110,ap , Yu.A. Tikhonov122b,122a , S. Timoshenko112 , P. Tipton183 , S. Tisserant101 , K. Todome165 , S. Todorova-Nova5 , S. Todt48 , J. Tojo87 , S. Tokár28a , K. Tokushuku81 , E. Tolley126 , K.G. Tomiwa33c , M. Tomoto117 , L. Tompkins153,q , K. Toms118 , B. Tong59 , P. Tornambe52 , E. Torrence131 , H. Torres48 , E. Torró Pastor148 , C. Tosciri135 , J. Toth101,ac , D.R. Tovey149 , C.J. Treado124 , T. Trefzger177 , F. Tresoldi156 , A. Tricoli29 , I.M. Trigger168a , S. Trincaz-Duvoid136 , W. Trischuk167 , B. Trocmé58 , A. Trofymov132 , C. Troncon68a , M. Trovatelli176 , F. Trovato156 , L. Truong33b , M. Trzebinski84 , A. Trzupek84 , F. Tsai46 , J.C-L. Tseng135 , P.V. Tsiareshka107,aj , A. Tsirigotis162 , N. Tsirintanis9 , V. Tsiskaridze155 , E.G. Tskhadadze159a , M. Tsopoulou162 , I.I. Tsukerman111 , V. Tsulaia18 , S. Tsuno81 , D. Tsybychev155 , Y. Tu63b , A. Tudorache27b , V. Tudorache27b , T.T. Tulbure27a , A.N. Tuna59 , S. Turchikhin79 , D. Turgeman180 , I. Turk Cakir4b,u , R.J. Turner21 , R.T. Turra68a , P.M. Tuts39 , S Tzamarias162 , E. Tzovara99 , G. Ucchielli47 , I. Ueda81 , M. Ughetto45a,45b , F. Ukegawa169 , G. Unal36 , A. Undrus29 , G. Unel171 , F.C. Ungaro104 , Y. Unno81 , K. Uno163 , J. Urban28b , P. Urquijo104 , G. Usai8 , J. Usui81 , L. Vacavant101 , V. Vacek142 , B. Vachon103 , K.O.H. Vadla134 , A. Vaidya94 , C. Valderanis114 , E. Valdes Santurio45a,45b , M. Valente54 , S. Valentinetti23b,23a , A. Valero174 , L. Valéry46 , R.A. Vallance21 , A. Vallier5 , J.A. Valls Ferrer174 , T.R. Van Daalen14 , P. Van Gemmeren6 , I. Van Vulpen120 , M. Vanadia73a,73b , W. Vandelli36 , A. Vaniachine166 , R. Vari72a , E.W. Varnes7 , C. Varni55b,55a , T. Varol42 , D. Varouchas132 , K.E. Varvell157 , G.A. Vasquez147b , J.G. Vasquez183 , F. Vazeille38 , D. Vazquez Furelos14 , T. Vazquez Schroeder36 , J. Veatch53 , V. Vecchio74a,74b , L.M. Veloce167 , F. Veloso140a,140c , S. Veneziano72a , A. Ventura67a,67b , N. Venturi36 , A. Verbytskyi115 , V. Vercesi70a , M. Verducci74a,74b , C.M. Vergel Infante78 , C. Vergis24 , W. Verkerke120 , A.T. Vermeulen120 , J.C. Vermeulen120 , M.C. Vetterli152,aw , N. Viaux Maira147b , M. Vicente Barreto Pinto54 , I. Vichou173,∗ , T. Vickey149 , O.E. Vickey Boeriu149 , G.H.A. Viehhauser135 , L. Vigani135 , M. Villa23b,23a , M. Villaplana Perez68a,68b , E. Vilucchi51 , M.G. Vincter34 , V.B. Vinogradov79 , A. Vishwakarma46 , C. Vittori23b,23a , I. Vivarelli156 , M. Vogel182 , P. Vokac142 , G. Volpi14 , S.E. von Buddenbrock33c , E. Von Toerne24 , V. Vorobel143 , K. Vorobev112 , M. Vos174 , J.H. Vossebeld90 , N. Vranjes16 , M. Vranjes Milosavljevic16 , V. Vrba142 , M. Vreeswijk120 , T. Šfiligoj91 , R. Vuillermet36 , I. Vukotic37 , T. Ženiš28a , L. Živković16 , P. Wagner24 , W. Wagner182 , J. Wagner-Kuhr114 , H. Wahlberg88 , S. Wahrmund48 , K. Wakamiya82 , V.M. Walbrecht115 , J. Walder89 , R. Walker114 , S.D. Walker93 , W. Walkowiak151 , V. Wallangen45a,45b , A.M. Wang59 , C. Wang60b , F. Wang181 , H. Wang18 , H. Wang3 , J. Wang157 , J. Wang61b , P. Wang42 , Q. Wang128 , R.-J. Wang136 , – 78 – R. Wang60a , R. Wang6 , S.M. Wang158 , W.T. Wang60a , W. Wang15c,ae , W.X. Wang60a,ae , Y. Wang60a,am , Z. Wang60c , C. Wanotayaroj46 , A. Warburton103 , C.P. Ward32 , D.R. Wardrope94 , A. Washbrook50 , A.T. Watson21 , M.F. Watson21 , G. Watts148 , B.M. Waugh94 , A.F. Webb11 , S. Webb99 , C. Weber183 , M.S. Weber20 , S.A. Weber34 , S.M. Weber61a , A.R. Weidberg135 , J. Weingarten47 , M. Weirich99 , C. Weiser52 , P.S. Wells36 , T. Wenaus29 , T. Wengler36 , S. Wenig36 , N. Wermes24 , M.D. Werner78 , P. Werner36 , M. Wessels61a , T.D. Weston20 , K. Whalen131 , N.L. Whallon148 , A.M. Wharton89 , A.S. White105 , A. White8 , M.J. White1 , R. White147b , D. Whiteson171 , B.W. Whitmore89 , F.J. Wickens144 , W. Wiedenmann181 , M. Wielers144 , C. Wiglesworth40 , L.A.M. Wiik-Fuchs52 , F. Wilk100 , H.G. Wilkens36 , L.J. Wilkins93 , H.H. Williams137 , S. Williams32 , C. Willis106 , S. Willocq102 , J.A. Wilson21 , I. Wingerter-Seez5 , E. Winkels156 , F. Winklmeier131 , O.J. Winston156 , B.T. Winter52 , M. Wittgen153 , M. Wobisch95 , JHEP05(2019)142 A. Wolf99 , T.M.H. Wolf120 , R. Wolff101 , J. Wollrath52 , M.W. 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Zwalinski36 1 Department of Physics, University of Adelaide, Adelaide; Australia 2 Physics Department, SUNY Albany, Albany NY; United States of America 3 Department of Physics, University of Alberta, Edmonton AB; Canada 4 (a) Department of Physics, Ankara University, Ankara;(b) Istanbul Aydin University, Istanbul;(c) Division of Physics, TOBB University of Economics and Technology, Ankara; Turkey 5 LAPP, Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS/IN2P3, Annecy; France 6 High Energy Physics Division, Argonne National Laboratory, Argonne IL; United States of America 7 Department of Physics, University of Arizona, Tucson AZ; United States of America 8 Department of Physics, University of Texas at Arlington, Arlington TX; United States of America 9 Physics Department, National and Kapodistrian University of Athens, Athens; Greece 10 Physics Department, National Technical University of Athens, Zografou; Greece 11 Department of Physics, University of Texas at Austin, Austin TX; United States of America 12 (a) Bahcesehir University, Faculty of Engineering and Natural Sciences, Istanbul; (b) Istanbul Bilgi University, Faculty of Engineering and Natural Sciences, Istanbul;(c) Department of Physics, Bogazici University, Istanbul;(d) Department of Physics Engineering, Gaziantep University, Gaziantep; Turkey 13 Institute of Physics, Azerbaijan Academy of Sciences, Baku; Azerbaijan 14 Institut de Fı́sica d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Barcelona; Spain – 79 – 15 (a) Institute of High Energy Physics, Chinese Academy of Sciences, Beijing;(b) Physics Department, Tsinghua University, Beijing;(c) Department of Physics, Nanjing University, Nanjing;(d) University of Chinese Academy of Science (UCAS), Beijing; China 16 Institute of Physics, University of Belgrade, Belgrade; Serbia 17 Department for Physics and Technology, University of Bergen, Bergen; Norway 18 Physics Division, Lawrence Berkeley National Laboratory and University of California, Berkeley CA; United States of America 19 Institut für Physik, Humboldt Universität zu Berlin, Berlin; Germany 20 Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics, University of Bern, Bern; Switzerland 21 School of Physics and Astronomy, University of Birmingham, Birmingham; United Kingdom 22 Facultad de Ciencias y Centro de Investigaciónes, Universidad Antonio Nariño, Bogota; Colombia JHEP05(2019)142 23 (a) INFN Bologna and Universita’ di Bologna, Dipartimento di Fisica;(b) INFN Sezione di Bologna; Italy 24 Physikalisches Institut, Universität Bonn, Bonn; Germany 25 Department of Physics, Boston University, Boston MA; United States of America 26 Department of Physics, Brandeis University, Waltham MA; United States of America 27 (a) Transilvania University of Brasov, Brasov;(b) Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest;(c) Department of Physics, Alexandru Ioan Cuza University of Iasi, Iasi;(d) National Institute for Research and Development of Isotopic and Molecular Technologies, Physics Department, Cluj-Napoca;(e) University Politehnica Bucharest, Bucharest;(f ) West University in Timisoara, Timisoara; Romania 28 (a) Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava;(b) Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice; Slovak Republic 29 Physics Department, Brookhaven National Laboratory, Upton NY; United States of America 30 Departamento de Fı́sica, Universidad de Buenos Aires, Buenos Aires; Argentina 31 California State University, CA; United States of America 32 Cavendish Laboratory, University of Cambridge, Cambridge; United Kingdom 33 (a) Department of Physics, University of Cape Town, Cape Town;(b) Department of Mechanical Engineering Science, University of Johannesburg, Johannesburg;(c) School of Physics, University of the Witwatersrand, Johannesburg; South Africa 34 Department of Physics, Carleton University, Ottawa ON; Canada 35 (a) Faculté des Sciences Ain Chock, Réseau Universitaire de Physique des Hautes Energies - Université Hassan II, Casablanca;(b) Faculté des Sciences, Université Ibn-Tofail, Kénitra;(c) Faculté des Sciences Semlalia, Université Cadi Ayyad, LPHEA-Marrakech;(d) Faculté des Sciences, Université Mohamed Premier and LPTPM, Oujda;(e) Faculté des sciences, Université Mohammed V, Rabat; Morocco 36 CERN, Geneva; Switzerland 37 Enrico Fermi Institute, University of Chicago, Chicago IL; United States of America 38 LPC, Université Clermont Auvergne, CNRS/IN2P3, Clermont-Ferrand; France 39 Nevis Laboratory, Columbia University, Irvington NY; United States of America 40 Niels Bohr Institute, University of Copenhagen, Copenhagen; Denmark 41 (a) Dipartimento di Fisica, Università della Calabria, Rende;(b) INFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati; Italy 42 Physics Department, Southern Methodist University, Dallas TX; United States of America 43 Physics Department, University of Texas at Dallas, Richardson TX; United States of America 44 National Centre for Scientific Research “Demokritos”, Agia Paraskevi; Greece 45 (a) Department of Physics, Stockholm University;(b) Oskar Klein Centre, Stockholm; Sweden 46 Deutsches Elektronen-Synchrotron DESY, Hamburg and Zeuthen; Germany 47 Lehrstuhl für Experimentelle Physik IV, Technische Universität Dortmund, Dortmund; Germany 48 Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden; Germany – 80 – 49 Department of Physics, Duke University, Durham NC; United States of America 50 SUPA - School of Physics and Astronomy, University of Edinburgh, Edinburgh; United Kingdom 51 INFN e Laboratori Nazionali di Frascati, Frascati; Italy 52 Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg; Germany 53 II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen; Germany 54 Département de Physique Nucléaire et Corpusculaire, Université de Genève, Genève; Switzerland 55 (a) Dipartimento di Fisica, Università di Genova, Genova;(b) INFN Sezione di Genova; Italy 56 II. Physikalisches Institut, Justus-Liebig-Universität Giessen, Giessen; Germany 57 SUPA - School of Physics and Astronomy, University of Glasgow, Glasgow; United Kingdom 58 LPSC, Université Grenoble Alpes, CNRS/IN2P3, Grenoble INP, Grenoble; France 59 Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge MA; United States of America JHEP05(2019)142 60 (a) Department of Modern Physics and State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei;(b) Institute of Frontier and Interdisciplinary Science and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Qingdao;(c) School of Physics and Astronomy, Shanghai Jiao Tong University, KLPPAC-MoE, SKLPPC, Shanghai;(d) Tsung-Dao Lee Institute, Shanghai; China 61 (a) Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg; (b) Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg; Germany 62 Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima; Japan 63 (a) Department of Physics, Chinese University of Hong Kong, Shatin, N.T., Hong Kong;(b) Department of Physics, University of Hong Kong, Hong Kong;(c) Department of Physics and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong; China 64 Department of Physics, National Tsing Hua University, Hsinchu; Taiwan 65 Department of Physics, Indiana University, Bloomington IN; United States of America 66 (a) INFN Gruppo Collegato di Udine, Sezione di Trieste, Udine;(b) ICTP, Trieste;(c) Dipartimento Politecnico di Ingegneria e Architettura, Università di Udine, Udine; Italy 67 (a) INFN Sezione di Lecce;(b) Dipartimento di Matematica e Fisica, Università del Salento, Lecce; Italy 68 (a) INFN Sezione di Milano;(b) Dipartimento di Fisica, Università di Milano, Milano; Italy 69 (a) INFN Sezione di Napoli;(b) Dipartimento di Fisica, Università di Napoli, Napoli; Italy 70 (a) INFN Sezione di Pavia;(b) Dipartimento di Fisica, Università di Pavia, Pavia; Italy 71 (a) INFN Sezione di Pisa;(b) Dipartimento di Fisica E. Fermi, Università di Pisa, Pisa; Italy 72 (a) INFN Sezione di Roma;(b) Dipartimento di Fisica, Sapienza Università di Roma, Roma; Italy 73 (a) INFN Sezione di Roma Tor Vergata;(b) Dipartimento di Fisica, Università di Roma Tor Vergata, Roma; Italy 74 (a) INFN Sezione di Roma Tre;(b) Dipartimento di Matematica e Fisica, Università Roma Tre, Roma; Italy 75 (a) INFN-TIFPA;(b) Università degli Studi di Trento, Trento; Italy 76 Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität, Innsbruck; Austria 77 University of Iowa, Iowa City IA; United States of America 78 Department of Physics and Astronomy, Iowa State University, Ames IA; United States of America 79 Joint Institute for Nuclear Research, Dubna; Russia 80 (a) Departamento de Engenharia Elétrica, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora;(b) Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro; (c) Universidade Federal de São João del Rei (UFSJ), São João del Rei;(d) Instituto de Fı́sica, Universidade de São Paulo, São Paulo; Brazil 81 KEK, High Energy Accelerator Research Organization, Tsukuba; Japan 82 Graduate School of Science, Kobe University, Kobe; Japan 83 (a) AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow;(b) Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow; Poland – 81 – 84 Institute of Nuclear Physics Polish Academy of Sciences, Krakow; Poland 85 Faculty of Science, Kyoto University, Kyoto; Japan 86 Kyoto University of Education, Kyoto; Japan 87 Research Center for Advanced Particle Physics and Department of Physics, Kyushu University, Fukuoka; Japan 88 Instituto de Fı́sica La Plata, Universidad Nacional de La Plata and CONICET, La Plata; Argentina 89 Physics Department, Lancaster University, Lancaster; United Kingdom 90 Oliver Lodge Laboratory, University of Liverpool, Liverpool; United Kingdom 91 Department of Experimental Particle Physics, Jožef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana; Slovenia 92 School of Physics and Astronomy, Queen Mary University of London, London; United Kingdom 93 Department of Physics, Royal Holloway University of London, Egham; United Kingdom JHEP05(2019)142 94 Department of Physics and Astronomy, University College London, London; United Kingdom 95 Louisiana Tech University, Ruston LA; United States of America 96 Fysiska institutionen, Lunds universitet, Lund; Sweden 97 Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), Villeurbanne; France 98 Departamento de Fı́sica Teorica C-15 and CIAFF, Universidad Autónoma de Madrid, Madrid; Spain 99 Institut für Physik, Universität Mainz, Mainz; Germany 100 School of Physics and Astronomy, University of Manchester, Manchester; United Kingdom 101 CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille; France 102 Department of Physics, University of Massachusetts, Amherst MA; United States of America 103 Department of Physics, McGill University, Montreal QC; Canada 104 School of Physics, University of Melbourne, Victoria; Australia 105 Department of Physics, University of Michigan, Ann Arbor MI; United States of America 106 Department of Physics and Astronomy, Michigan State University, East Lansing MI; United States of America 107 B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk; Belarus 108 Research Institute for Nuclear Problems of Byelorussian State University, Minsk; Belarus 109 Group of Particle Physics, University of Montreal, Montreal QC; Canada 110 P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow; Russia 111 Institute for Theoretical and Experimental Physics of the National Research Centre Kurchatov Institute, Moscow; Russia 112 National Research Nuclear University MEPhI, Moscow; Russia 113 D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow; Russia 114 Fakultät für Physik, Ludwig-Maximilians-Universität München, München; Germany 115 Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München; Germany 116 Nagasaki Institute of Applied Science, Nagasaki; Japan 117 Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya; Japan 118 Department of Physics and Astronomy, University of New Mexico, Albuquerque NM; United States of America 119 Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen; Netherlands 120 Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam; Netherlands 121 Department of Physics, Northern Illinois University, DeKalb IL; United States of America 122 (a) Budker Institute of Nuclear Physics and NSU, SB RAS, Novosibirsk;(b) Novosibirsk State University Novosibirsk; Russia 123 Institute for High Energy Physics of the National Research Centre Kurchatov Institute, Protvino; Russia – 82 – 124 Department of Physics, New York University, New York NY; United States of America 125 Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo; Japan 126 Ohio State University, Columbus OH; United States of America 127 Faculty of Science, Okayama University, Okayama; Japan 128 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman OK; United States of America 129 Department of Physics, Oklahoma State University, Stillwater OK; United States of America 130 Palacký University, RCPTM, Joint Laboratory of Optics, Olomouc; Czech Republic 131 Center for High Energy Physics, University of Oregon, Eugene OR; United States of America 132 LAL, Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay; France 133 Graduate School of Science, Osaka University, Osaka; Japan 134 Department of Physics, University of Oslo, Oslo; Norway JHEP05(2019)142 135 Department of Physics, Oxford University, Oxford; United Kingdom 136 LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3, Paris; France 137 Department of Physics, University of Pennsylvania, Philadelphia PA; United States of America 138 Konstantinov Nuclear Physics Institute of National Research Centre “Kurchatov Institute”, PNPI, St. Petersburg; Russia 139 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh PA; United States of America 140 (a) Laboratório de Instrumentação e Fı́sica Experimental de Partı́culas - LIP; (b) Departamento de Fı́sica, Faculdade de Ciências, Universidade de Lisboa, Lisboa; (c) Departamento de Fı́sica, Universidade de Coimbra, Coimbra;(d) Centro de Fı́sica Nuclear da Universidade de Lisboa, Lisboa;(e) Departamento de Fı́sica, Universidade do Minho, Braga;(f ) Universidad de Granada, Granada (Spain);(g) Dep Fı́sica and CEFITEC of Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica; Portugal 141 Institute of Physics of the Czech Academy of Sciences, Prague; Czech Republic 142 Czech Technical University in Prague, Prague; Czech Republic 143 Charles University, Faculty of Mathematics and Physics, Prague; Czech Republic 144 Particle Physics Department, Rutherford Appleton Laboratory, Didcot; United Kingdom 145 IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette; France 146 Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz CA; United States of America 147 (a) Departamento de Fı́sica, Pontificia Universidad Católica de Chile, Santiago; (b) Departamento de Fı́sica, Universidad Técnica Federico Santa Marı́a, Valparaı́so; Chile 148 Department of Physics, University of Washington, Seattle WA; United States of America 149 Department of Physics and Astronomy, University of Sheffield, Sheffield; United Kingdom 150 Department of Physics, Shinshu University, Nagano; Japan 151 Department Physik, Universität Siegen, Siegen; Germany 152 Department of Physics, Simon Fraser University, Burnaby BC; Canada 153 SLAC National Accelerator Laboratory, Stanford CA; United States of America 154 Physics Department, Royal Institute of Technology, Stockholm; Sweden 155 Departments of Physics and Astronomy, Stony Brook University, Stony Brook NY; United States of America 156 Department of Physics and Astronomy, University of Sussex, Brighton; United Kingdom 157 School of Physics, University of Sydney, Sydney; Australia 158 Institute of Physics, Academia Sinica, Taipei; Taiwan 159 (a) E. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi; (b) High Energy Physics Institute, Tbilisi State University, Tbilisi; Georgia 160 Department of Physics, Technion, Israel Institute of Technology, Haifa; Israel 161 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv; Israel 162 Department of Physics, Aristotle University of Thessaloniki, Thessaloniki; Greece – 83 – 163 International Center for Elementary Particle Physics and Department of Physics, University of Tokyo, Tokyo; Japan 164 Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo; Japan 165 Department of Physics, Tokyo Institute of Technology, Tokyo; Japan 166 Tomsk State University, Tomsk; Russia 167 Department of Physics, University of Toronto, Toronto ON; Canada 168 (a) TRIUMF, Vancouver BC;(b) Department of Physics and Astronomy, York University, Toronto ON; Canada 169 Division of Physics and Tomonaga Center for the History of the Universe, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba; Japan 170 Department of Physics and Astronomy, Tufts University, Medford MA; United States of America 171 Department of Physics and Astronomy, University of California Irvine, Irvine CA; United States of JHEP05(2019)142 America 172 Department of Physics and Astronomy, University of Uppsala, Uppsala; Sweden 173 Department of Physics, University of Illinois, Urbana IL; United States of America 174 Instituto de Fı́sica Corpuscular (IFIC), Centro Mixto Universidad de Valencia - CSIC, Valencia; Spain 175 Department of Physics, University of British Columbia, Vancouver BC; Canada 176 Department of Physics and Astronomy, University of Victoria, Victoria BC; Canada 177 Fakultät für Physik und Astronomie, Julius-Maximilians-Universität Würzburg, Würzburg; Germany 178 Department of Physics, University of Warwick, Coventry; United Kingdom 179 Waseda University, Tokyo; Japan 180 Department of Particle Physics, Weizmann Institute of Science, Rehovot; Israel 181 Department of Physics, University of Wisconsin, Madison WI; United States of America 182 Fakultät für Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal; Germany 183 Department of Physics, Yale University, New Haven CT; United States of America 184 Yerevan Physics Institute, Yerevan; Armenia a Also at Borough of Manhattan Community College, City University of New York, New York NY; United States of America b Also at Centre for High Performance Computing, CSIR Campus, Rosebank, Cape Town; South Africa c Also at CERN, Geneva; Switzerland d Also at CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille; France e Also at Département de Physique Nucléaire et Corpusculaire, Université de Genève, Genève; Switzerland f Also at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona; Spain g Also at Departamento de Fı́sica, Instituto Superior Técnico, Universidade de Lisboa, Lisboa; Portugal h Also at Department of Applied Physics and Astronomy, University of Sharjah, Sharjah; United Arab Emirates i Also at Department of Financial and Management Engineering, University of the Aegean, Chios; Greece j Also at Department of Physics and Astronomy, University of Louisville, Louisville, KY; United States of America k Also at Department of Physics and Astronomy, University of Sheffield, Sheffield; United Kingdom l Also at Department of Physics, California State University, East Bay; United States of America m Also at Department of Physics, California State University, Fresno; United States of America n Also at Department of Physics, California State University, Sacramento; United States of America o Also at Department of Physics, King’s College London, London; United Kingdom – 84 – p Also at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg; Russia q Also at Department of Physics, Stanford University, Stanford CA; United States of America r Also at Department of Physics, University of Fribourg, Fribourg; Switzerland s Also at Department of Physics, University of Michigan, Ann Arbor MI; United States of America t Also at Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow; Russia u Also at Giresun University, Faculty of Engineering, Giresun; Turkey v Also at Graduate School of Science, Osaka University, Osaka; Japan w Also at Hellenic Open University, Patras; Greece x Also at Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest; Romania y Also at Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona; Spain z Also at Institut für Experimentalphysik, Universität Hamburg, Hamburg; Germany JHEP05(2019)142 aa Also at Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen; Netherlands ab Also at Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia; Bulgaria ac Also at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest; Hungary ad Also at Institute of Particle Physics (IPP); Canada ae Also at Institute of Physics, Academia Sinica, Taipei; Taiwan af Also at Institute of Physics, Azerbaijan Academy of Sciences, Baku; Azerbaijan ag Also at Institute of Theoretical Physics, Ilia State University, Tbilisi; Georgia ah Also at Instituto de Fisica Teorica, IFT-UAM/CSIC, Madrid; Spain ai Also at Istanbul University, Dept. of Physics, Istanbul; Turkey aj Also at Joint Institute for Nuclear Research, Dubna; Russia ak Also at LAL, Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay; France al Also at Louisiana Tech University, Ruston LA; United States of America am Also at LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3, Paris; France an Also at Manhattan College, New York NY; United States of America ao Also at Moscow Institute of Physics and Technology State University, Dolgoprudny; Russia ap Also at National Research Nuclear University MEPhI, Moscow; Russia aq Also at Physics Department, An-Najah National University, Nablus; Palestine ar Also at Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg; Germany as Also at School of Physics, Sun Yat-sen University, Guangzhou; China at Also at The City College of New York, New York NY; United States of America au Also at The Collaborative Innovation Center of Quantum Matter (CICQM), Beijing; China av Also at Tomsk State University, Tomsk, and Moscow Institute of Physics and Technology State University, Dolgoprudny; Russia aw Also at TRIUMF, Vancouver BC; Canada ax Also at Universita di Napoli Parthenope, Napoli; Italy ∗ Deceased – 85 –