Physics Letters B 796 (2019) 68–87 Contents lists available at ScienceDirect Physics Letters B www.elsevier.com/locate/physletb Search for high-mass dilepton −1 √ resonances using 139 fb of pp collision data collected at s = 13 TeV with the ATLAS detector .The ATLAS Collaboration  a r t i c l e i n f o a b s t r a c t Article history: A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV is Received 18 March 2019 presented. The data Received in revised form 23 May 2019 √ were recorded by the ATLAS experiment in proton–proton collisions at a centre-of- mass energy of s = 13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated Accepted 5 July 2019 luminosity of 139 fb−1 . A functional form is fitted to the dilepton invariant-mass distribution to model Available online 10 July 2019 Editor: M. Doser the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times branching ratio for various resonance width hypotheses. The derived limits are shown to be applicable to spin-0, spin-1 and spin-2 signal hypotheses. For a set of benchmark models, the limits are converted into lower  boson. Also presented are limits limits on the resonance mass and reach 4.5 TeV for the E6 -motivated Z ψ on Heavy Vector Triplet model couplings. © 2019 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3 . 1. Introduction  Z HVT boson is a neutral member of a new SU(2) gauge group, i.e. part of a triplet and cannot exist without two new charged heavy ± Searches in the dilepton (dielectron and dimuon) final state bosons, W HVT , with which it is nearly degenerate in mass. New have a long and illustrious history with the discovery of the J /ψ spin-2 resonances, excited states of the graviton, are introduced meson in 1974 [1,2] and ϒ meson in 1977 [3] as well as the Z in the Randall–Sundrum model [10] with a warped extra dimen- boson in 1983 [4,5]. As these were key steps which led to the es- sion. In experimental terms the described scenarios would result tablishment of the Standard Model (SM) of particle physics, the in a local excess of signal candidates over a smoothly falling dilep- study of the same final state could help to pave the way to a bet- ton mass spectrum. This search has a clean experimental signature ter understanding of the physics processes beyond it. with a fully reconstructable final state and excellent detection effi- Various models predict resonances which decay into dileptons ciency. and can be categorised according to their spin. A new high-mass This Letter presents a search for a new resonance decaying spin-0 resonance, H , introduced as part of an extended scalar into two electrons or two muons in 139 fb−1 of data collected in sector in some models, such as the Minimal Supersymmetric SM proton–proton (pp) collisions at the LHC at a centre-of-mass en- √ (MSSM) [6], has higher decay rate into a pair of muons rather than ergy s = 13 TeV. Previous searches with 36.1 fb−1 of pp collision √ electrons. The majority of searches for new neutral high-mass res- data at s = 13 TeV conducted by the ATLAS and CMS experi- onances have focused on a new spin-1 vector boson, generally re- ments [11,12] showed no significant excess and led to lower limits  boson. The analysis pre- ferred to as Z  , that appears in models with extended gauge sym- of up to 3.8 TeV for the mass of the Z ψ metries. Typical benchmark models include the Sequential Stan- sented in this Letter, compared with that published in Ref. [11],  dard Model Z SSM boson [7], which has the same fermion couplings benefits from: a factor of four increase in integrated luminosity; as the SM Z boson, a Z χ  and a Z  boson of an E -motivated ψ 6 several improvements in the reconstruction software, including the  Grand Unification model [8], or a Z HVT boson of the Heavy Vec- use of a new dynamical, topological cell-clustering algorithm for tor Triplet model [9]. In the first two models, the Z  boson is a electron reconstruction [13] and an improved treatment of the singlet, associated with a new U(1) gauge group, and generally its relative alignment of the inner tracker and the muon tracking de- couplings to the SM W and Z bosons are assumed to be zero. The tectors in the muon reconstruction; the use of invariant-mass side- bands of the expected signal in data to constrain the fit parameters of the background distribution, which is described by a smooth  E-mail address: atlas.publications@cern.ch. functional form instead of relying on simulation; and a generic https://doi.org/10.1016/j.physletb.2019.07.016 0370-2693/© 2019 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3 . The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 69 Table 1 The event generators used for simulation of the signal and background processes. The acronyms ME and PS stand for matrix element and parton shower. The top-quark mass is set to 172.5 GeV. ME Generator and ME PDFs PS and non-perturbative effect with PDFs Background process NLO Drell–Yan Powheg-Box [23,24], CT10 [25], Photos Pythia v8.186 [26], CTEQ6L1 [27,28], EvtGen1.2.0 t t̄ Powheg-Box, NNPDF3.0NLO [29] Pythia v8.230, NNPDF23LO [30], EvtGen1.6.0 Single top s-channel, W t Powheg-Box, NNPDF3.0NLO Pythia v8.230, NNPDF23LO, EvtGen1.6.0 Single top t-channel Powheg-Box, NNPDF3.04fNLO, MadSpin Pythia v8.230, NNPDF23LO, EvtGen1.6.0 Diboson (W W , W Z and Z Z ) Sherpa 2.1.1 [31], CT10 Sherpa 2.1.1, CT10 Signal process LO Drell–Yan Pythia v8.186, NNPDF23LO Pythia v8.186, NNPDF23LO, EvtGen1.2.0 Randall–Sundrum G ∗ →  Pythia v8.210, NNPDF23LO Pythia v8.210, NNPDF23LO, EvtGen1.2.0 MSSM gg → H →  Powheg-Box, CT10 Pythia v8.212, CTEQ6L1, EvtGen1.2.0 signal line shape described by a non-relativistic Breit–Wigner func- ground processes are used to determine appropriate functions to tion convolved with the detector resolution, which simplifies rein- fit the data, study background compositions and to evaluate the terpretations of the result. signal efficiency. The main backgrounds in decreasing order of im- portance are Drell–Yan (DY), top-quark pair (t t̄), single-top-quark 2. ATLAS detector and diboson production. Multi-jet and W + jets processes in the dielectron channel are estimated with a data-driven method [11]. ATLAS [14–16] is a multipurpose detector with a forward– Multi-jet and W + jets processes in the dimuon channel as well as backward symmetric cylindrical geometry with respect to the LHC processes with τ -leptons in both channels have a negligible impact beam axis.1 The innermost layers consist of tracking detectors in and are not considered. The Monte Carlo (MC) event generators for the pseudorapidity range |η| < 2.5. This inner detector (ID) is sur- the hard-scatter process, showering and parton distribution func- rounded by a thin superconducting solenoid that provides a 2 T tions (PDFs) are listed in Table 1. The ‘afterburner’ generators such axial magnetic field. It is enclosed by the electromagnetic and as Photos [20] for the final-state photon radiation (FSR) modelling, hadronic calorimeters, which cover |η| < 4.9. The outermost layers MadSpin [21] to preserve top-quark spin correlations, and Evt- of ATLAS consist of an external muon spectrometer (MS) within Gen [22], used for the modelling of c- and b-hadron decays, are |η| < 2.7, incorporating three large toroidal magnetic assemblies also reported. with eight coils each. The field integral of the toroids ranges be- The DY [32] and diboson [33] samples are generated in slices tween 2.0 and 6.0 Tm for most of the acceptance. The MS includes of dilepton mass to increase the sample size in the high-mass re- precision tracking chambers and fast detectors for triggering. A gion. Next-to-next-to-leading-order (NNLO) corrections in quantum two-level trigger system [17] reduces the recorded event rate to chromodynamic (QCD) theory and next-to-leading-order (NLO) an average of 1 kHz. corrections in electroweak (EW) theory, are calculated and ap- plied to the DY events. The corrections are computed with VRAP 3. Data and simulation v0.9 [34] and the CT14 NNLO PDF set [35] in the case of QCD ef- fects whereas they are computed with MCSANC [36] in the case of The dataset used in this analysis was collected during LHC quantum electrodynamic effects due to initial state radiation, in- Run 2 in stable beam conditions and with all detector systems op- terference between initial and final state radiation, and Sudakov erating normally. The event quality was checked to remove events logarithm single-loop corrections. The top-quark samples [37] are with noise bursts or coherent noise in the calorimeters. Events normalised to the cross-sections calculated at NNLO in QCD includ- in the dielectron channel were recorded using a dielectron trig- ing resummation of the next-to-next-to-leading logarithmic soft ger based on the ‘very loose’ or ‘loose’ identification criteria [17] gluon terms as provided by Top++2.0 [38]. with transverse energy (E T ) thresholds between 12 and 24 GeV for Spin-1 signal templates are obtained by a matrix-element both electrons, depending on the data-taking period. Events in the reweighting [11] of the leading-order (LO) DY samples generated dimuon channel are required to pass at least one of two single- in slices of dilepton mass. These signal templates are used only muon triggers: the first requires a transverse momentum (p T ) of at for cross-section and efficiency calculations. The relative natural least 50 GeV, while the second has a threshold lowered to 26 GeV width ( Z  /m Z  ) for the benchmark models considered varies be- tween 0.5% for Z ψ  and 3% for Z  but requires the muon candidate to be isolated [17]. The integrated SSM . Interference effects between luminosity of the dataset is determined to be 139.0 ± 2.4 fb−1 , the resonant signal and the background processes are neglected. following a methodology similar to that detailed in Ref. [18], and Higher-order QCD corrections for all the spin-1 signals are com- using the LUCID-2 detector for the baseline luminosity measure- puted with the same methodology as for the DY background. For ments [19], from calibration of the luminosity scale using x-y the HVT model, these corrections are not applied, which ensures beam-separation scans. consistent treatment with the other signal channels in an eventual While the search in this analysis is carried out entirely in a combination, similar to that described in Ref. [39]. Electroweak data-driven way, simulated event samples for the signal and back- corrections are not applied to the signal samples due to their large model dependence. Spin-0 signal efficiencies are obtained from samples of the MSSM gluon–gluon fusion production of a heavy 1 ATLAS uses a right-handed coordinate system with its origin at the nominal Higgs boson decaying into dilepton pairs, g g → H → , produced interaction point (IP) in the centre of the detector and the z-axis along the beam in the mass range m H = 400–1000 GeV and with relative natural pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis width ( H /m H ) varying between zero and 20%. Spin-2 signal ef- points upwards. Cylindrical coordinates (r , φ) are used in the transverse plane, φ being the azimuthal angle around the z-axis. The pseudorapidity is defined in terms ficiencies are obtained from Randall–Sundrum graviton G ∗ →  polar angle θ as η = − ln tan(θ/2). Angular distance is measured in units of of the  samples produced in the mass range m G ∗ = 750–5000 GeV and R ≡ ( η)2 + ( φ)2 . with coupling strengths, k/mPl , of 0.1, 0.2 and 0.3, where k is a 70 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 scale that defines the warp factor of the extra dimension and mPl lation efficiency, uniform in η , using a combination of track and is the reduced Planck mass. calorimeter isolation requirements [44]. For muons, the summed Simulated event samples include the effect of multiple pp in- scalar p T of good-quality tracks with p T > 1 GeV originating from teractions in the same or neighbouring bunch crossings. These the primary vertex within a cone of variable size2 R around effects are collectively referred to as pile-up. The simulation of the muon, but excluding the muon-candidate track itself, must be pile-up collisions was performed with Pythia v8.186 using the less than 6% of the p T of the muon candidate. The efficiency of ATLAS A3 set of tuned parameters [40] and the NNPDF23LO this selection is above 99% for both electrons and muons with PDF set, and weighted to reproduce the average number of pile- p T > 60 GeV. Corrections are applied to electron (muon) candi- up interactions per bunch crossing observed in data. The gener- dates to match the energy (momentum) scale and resolution be- ated events were passed through a full detector simulation [41] tween simulation and data. These corrections are derived in an based on Geant 4 [42]. Spin-0 and spin-2 MC signal samples energy independent way for electrons [46]. For muons, the cor- were produced with a fast parameterisation of the calorimeter re- rection is determined as a function of p T up to 300 GeV, from a fit sponse [43]. to Z → μμ data with templates derived from simulation [45]. At Very large generator-level-only MC samples (with more than 55 high transverse momentum, the calibrations are dominated by cor- times the data events) for NLO DY events are used for the back- rections extracted from alignment studies, using special runs with ground studies described in Section 6. These samples could not be the toroidal magnetic field off. Corrections to the lepton efficien- produced with the full detector simulation due to the large num- cies in the simulation are derived from the data for electron E T ber of events required. (muon p T ) up to 150 (200) GeV [44,45]. The simulation is used to extrapolate to higher electron E T (muon p T ) and to study system- 4. Event selection atic effects. The events are required to contain at least two same-flavour The selection of dilepton events closely follows that described leptons. If additional leptons are present in the event, the two in Ref. [11]. An event is selected if at least one pp interaction ver- same-flavour leptons with the largest E T (p T ) in the electron tex is reconstructed. The primary vertex is chosen to be the vertex (muon) channel are selected to form the dilepton pair. If two with the highest summed p 2T of tracks with transverse momentum different-flavour pairs are found, the dielectron pair is kept, be- p T > 0.5 GeV which are associated with the vertex. cause of the better resolution and higher efficiency for electrons. Electron candidates are reconstructed from ID tracks that are A selected muon pair is required to be oppositely charged. For matched to clusters of energy deposited in the electromagnetic an electron pair, the opposite-charge requirement is not applied calorimeter with energy deposition consistent with that of an because of the higher probability of charge misidentification for electromagnetic shower [44]. Reconstructed electrons must have high-E T electrons. The reconstructed mass of the dilepton sys- E T > 30 GeV, satisfy |η| < 2.47 in order to pass through the fine- tem after the full analysis selection, m , is required to be above granularity region of the EM calorimeter, and be outside the range 225 GeV to avoid the Z boson peak region, which cannot be de- 1.37 < |η| < 1.52 corresponding to the transition region between scribed by the same parameterisation as the high-mass part of the the barrel and endcap EM calorimeters. The calorimeter granularity dilepton distributions. in the excluded transition region is reduced, and the presence of significant additional inactive material degrades the electron iden- 5. Reconstructed dilepton mass modelling tification capabilities and energy resolution. The ‘medium’ electron working point used for the final selection has an identification The relative dilepton mass resolution is defined as (m − and reconstruction efficiency for prompt electrons above 92% for mtrue true true  )/m , where m is the generated dilepton mass at Born E T > 80 GeV. level before FSR. The mass resolution is parameterised as a sum Muon candidates are identified by matching ID tracks to tracks of a Gaussian distribution, which describes the detector response, reconstructed in the MS [45]. Muon candidates must have p T > and a Crystal Ball function composed of a secondary Gaussian 30 GeV and |η| < 2.5. To ensure optimal muon momentum res- distribution with a power-law low-mass tail, which accounts for olution at high p T , the ‘high p T ’ identification working point is bremsstrahlung effects in the dielectron channel or for the effect used. It requires at least three hits in each of three layers of pre- of poorly reconstructed muons. The parameterisation of the rela- cision tracking chambers in the MS, and specific regions of the tive dilepton mass resolution as a function of mtrue  is determined MS where the alignment is suboptimal are vetoed as a precaution. by a simultaneous fit of the function described above to NLO DY These requirements reject about 80% (13%) of the muon candidates MC events. The MC sample is separated in 200 mtrue bins of equal in (outside) the barrel–endcap overlap region, 1.01 < |η| < 1.1. The size on a logarithmic scale in the range of 130 GeV to 6 TeV. This muon ‘high p T ’ working point has an η -averaged efficiency of 69% procedure is repeated to evaluate the uncertainty on the fit param- at 1 TeV which decreases to 64% at 2.5 TeV due to increased oc- eters by shifting individually the lepton energy and momentum casional catastrophic energy loss at high p T . Additionally, a ‘good scale and resolutions by their uncertainties. muon’ selection requires that the uncertainty in the charge-to- momentum ratio of muon candidates is less than a p T -dependent 6. Signal and background modelling value. This selection is fully efficient below 1 TeV, but introduces an additional inefficiency of 7% at 2.5 TeV. A resonant signal is searched for by fitting the data dilepton Electron (muon) candidate tracks must be consistent with the mass distribution. The fit function consists of a smooth functional primary vertex both along the beamline, where the longitudinal form for the background, and a generic signal shape. The generic impact parameter z0 is required to satisfy | z0 sinθ| < 0.5 mm, and signal shapes are constructed from non-relativistic Breit–Wigner in the transverse plane, where the transverse impact parameter functions of various widths convolved with the detector resolu- significance |d0 /σ (d0 )| is required to be less than 5 (3). To re- tion, obtained as described in the previous section. The shape of duce background from misidentified jets as well as from light- and heavy-flavour hadron decays inside jets, lepton candidates are re- quired to be isolated. Electrons must pass the ‘gradient’ isolation 2 R has a maximum value of 0.3 and decreases as a function of p T as working point which targets an E T -dependent value of the iso- 10 GeV/p T [GeV]. The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 71 Table 2 The relative impact of ±1σ variation of systematic uncertainties on the signal yield in percent for zero (10%) relative width signals at the pole masses of 300 GeV, 2 and 5 TeV for dielectron and dimuon channels. Sources of uncertainties leading to an impact smaller than 0.5% on the signal yield at any point of the mass spectrum are not shown. A signal is injected at the cross-section limit. Uncertainty source for m X [GeV] Dielectron Dimuon 300 2000 5000 300 2000 5000 Spurious signal ±12.5 (12.0) ±4.6 (10.8) ±0.1 (1.0) ±11.7 (11.0) ±3.8 (3.5) ±2.1 (2.2)     +12 +12 +25 +25 Lepton identification ±1.6 (1.6) ±5.6 (5.6) ±5.6 (5.6) ±1.8 (1.8) −10 −10 −20 −20 Isolation ±0.3 (0.3) ±1.1 (1.2) ±1.1 (1.1) ±0.4 (0.4) ±0.4 (0.4) ±0.4 (0.5) Luminosity ±1.7 (1.7) ±1.7 (1.7) ±1.7 (1.7) ±1.7 (1.7) ±1.7 (1.7) ±1.7 (1.7)     −1.7 +1.0 −1.9 +1.7 +0.1 Electron energy scale −4.0 −1.8 −6.0 −2.9 −0.4 (±0.8) – – –     +7.9 +1.1 +9.0 +0.7 +0.4 Electron energy resolution −8.3 −0.9 −11.8 −0.5 −0.9 (±0.1) – – –       +0.8 +0.3 +0.9 +0.7 +0.6 +0.5 Muon ID resolution – – – −2.3 −0.8 −1.3 −1.1 −0.4 −0.3     +2.8 +1.0 +3.2 +2.6 Muon MS resolution – – – −3.8 −1.3 −3.0 −2.4 ±2.4 (2.1)     +9.0 +9.0 +55 +55 ‘Good muon’ requirement – – – ±0.6 (0.6) −8.2 −8.2 −35 −35 the dilepton invariant mass distribution for a signal resonance with In order to select the background functional form, a fit to the intrinsic width that is negligible compared with the detector res- dilepton mass background template is performed, under the signal olution (zero-width signal) is obtained from the mass resolution plus background hypothesis, for various functional forms, following only. the procedure outlined in Ref. [47]. The chosen functional form is To allow for a generic resonance search, a fiducial region at the one with the smallest absolute number of fitted signal events particle level is defined following the selection criteria applied (‘spurious signal’), which are determined as a function of m : to the reconstructed lepton candidates: each electron and muon  b 3 candidate needs to pass |η| < 2.5 and E T ( p T ) > 30 GeV, and the f  (m ) = f BW, Z (m ) · 1 − xc · x i=0 p i log(x) , (1) i dilepton mass has to satisfy mtrue > m X − 2 X , where m X and X √ represent the pole mass and width of a hypothetical resonance X , where x = m / s and parameters b and p i with i = 0, ..3 are respectively. This selection is added in order to reduce the model left free in the fit to data and independent for dielectron and dependence from off-shell effects. dimuon channels. The parameter c is 1 for the dielectron and The nominal combined reconstruction and identification effi- 1/3 for the dimuon channel. The function f BW, Z (m ) is a non- ciency in the fiducial region is extracted from the DY sample and relativistic Breit–Wigner function with m Z = 91.1876 GeV and thus assumes the kinematics of a spin-1 boson. For the dielec- Z = 2.4952 GeV [48]. The normalisation of the background func- tron (dimuon) channels, it varies from 64% (54%) at 225 GeV to tion is such that the integral a corresponds to the total number of 74% (38%) at 6 TeV for the zero-width signals. For a spin-1 sig- background events. To further validate this functional form an ex- nal with 10% relative width, the efficiency changes by less than tra degree of freedom (i = 4) is added to the fit function before 0.5% relative to a signal with zero width for both channels over the final data analysis, to check if it improves the likelihood value most of the considered invariant-mass range. Only above 5 TeV in of the fit by more than 2σ . To check the fit stability in the high- the dimuon channel are the variations as large as 2% in absolute mass region, signal injection tests are performed at various mass efficiency. For the spin-0 and spin-2 samples, width-related varia- points. No significant bias in the number of extracted signal events tions are below 1%. For the dielectron channel, spin-0 and spin-2 is observed. efficiencies are higher than the corresponding spin-1 values by at Uncertainties related to the background modelling are propa- most 4%. For the dimuon channel, efficiencies for spin-0 and spin-2 gated into the determination of the spurious signal. Smooth tem- signals are at most 1% lower than the corresponding spin-1 values. plates for systematic shape uncertainties are produced using the The systematic uncertainties of the overall efficiency are due to same procedure as for the nominal templates. The uncertainties the uncertainties in the trigger, isolation, identification, and recon- considered include variations due to PDFs [11] and normalisa- struction efficiencies. tion of the t t̄ background component [49]. Uncertainties on the The smooth functional form for the background is based on multi-jet and W + jet background contributions [11] are also con- fit performance studies on a MC background template. The asso- sidered in the dielectron channel. For the selected function, the ciated uncertainties are also estimated through these studies. In largest spurious signal (accounting for all systematic variations) is order to minimise the statistical uncertainties in this procedure, required to be less than 30% of the statistical uncertainty in the the background template for DY is produced from large-statistics fitted signal yield (from the background distribution) for the zero- samples simulated only at generator level and smeared by the ex- width signal. This criterion is relaxed to 50% for signals of greater perimental dilepton mass resolution, described in the previous sec- width. The systematic uncertainty of the background estimate is tion, with mass-dependent acceptance and efficiency corrections mass dependent and corresponds to a functional interpolation be- applied. A similar procedure is applied to the generator-level dilep- tween the highest maxima among the spurious-signal-yield distri- ton mass distribution in the t t̄ sample exploiting the larger number butions for all systematic variations. The spurious-signal yield is of events from the generator-level mass distribution. The distribu- calculated independently for the relative signal width assumptions tions from the diboson and single-top simulated samples and, in between zero and 10% in steps of 0.5%. the electron channel, a template for multi-jet and W + jet pro- The impact of systematic uncertainties on the signal yield is cesses are also considered. All MC-based contributions are scaled shown in Table 2. Only systematic uncertainties which change the by their respective cross-sections and summed together to obtain fitted signal yield by more than 0.5% at any point in the mass the background template for the choice of the smooth functional spectrum are considered. The largest systematic uncertainty at low form. mass in both channels originates from the spurious signals. The 72 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 Fig. 1. Distribution of the (a) dielectron and (b) dimuon invariant mass for events passing the full selection. Generic zero-width signal shapes, scaled to 20 times the value of the corresponding expected upper limit at 95% CL on the fiducial cross-section times branching ratio, with pole masses of m X = 1.34, 2 and 3 TeV as well as background-only fits are superimposed. The data points are plotted at the centre of each bin. The error bars indicate statistical uncertainties only. The differences between the data and the fit results in units of standard deviations of the statistical uncertainty are shown in the bottom panels. largest systematic uncertainty in the dielectron channel at high channel. The impact of this approximation on the mass limits is mass originates from the electron identification efficiency. The un- below 100 GeV. certainty associated with the ‘good muon’ requirement is dominant in the dimuon channel at high mass. This uncertainty is estimated 8. Results with a conservative approach in a dataset collected in 2015–2016, corresponding to 36 fb−1 , by comparing efficiencies obtained in The dilepton invariant-mass distributions for the events that data and in simulation. pass the full analysis selection are shown in Fig. 1. The event with highest reconstructed mass is a dielectron candidate with 7. Statistical analysis mee = 4.06 TeV, formed of two electrons with E T = 2.01 TeV and E T = 1.92 TeV in the barrel region of the calorimeter. The event The numbers of signal and background events, as a function of with highest reconstructed mass in the dimuon channel has an in- the signal mass and width hypothesis, are estimated from simul- variant mass of mμμ = 2.75 TeV. Both muon candidates are in the taneous maximum-likelihood fits of the signal-plus-background barrel section of the muon spectrometer and their transverse mo- models to the data m distribution. Systematic uncertainties are menta are p T = 1.82 TeV and p T = 1.04 TeV. included in the fits via nuisance parameters constrained by penalty The fit to data3 is performed in bins of 1 GeV and uses the terms which are either Gaussian (e.g. energy and momentum function in Eq. (1). In both channels, validation tests using the ex- scale uncertainties) or log-normal (efficiency and resolution un- tension of the functional form described in Section 6 did not yield certainties). Potential mismodelling of the background estimate is any significant improvement, so the function in Eq. (1) is used accounted for through an additional nuisance parameter allow- without modification. ing non-zero signal normalisation under the null hypothesis con- The probability that the data are compatible with the back- strained by the measured spurious signal. Dielectron and dimuon ground-only hypothesis is shown in Fig. 2 as a function of pole channels are considered both as independent channels and in a mass for zero-width signals. No significant excess is observed. The combined approach, under a lepton-flavour universality assump- largest deviations from the background-only hypothesis in the di- tion [7,8]. electron, dimuon and combined dilepton channels are observed at The significance of a signal is summarised by a p-value, the masses of 774 GeV, 267 GeV and 264 GeV for zero-width signals probability of observing an excess at least as signal-like as the one with a local p 0 of 2.9 σ , 2.4 σ and 2.3 σ and a global significance observed in data, in the absence of signal. The local p-value of of 0.1 σ , 0.3 σ , and zero, respectively. the background-only hypothesis (p 0 ) is determined from a profile- Fig. 3 shows the upper limits on the fiducial cross-section times likelihood-ratio-test statistic [50] as detailed in Ref. [51] in the branching ratio to two leptons of a single flavour for generic reso- asymptotic approximation. Global significance values are also com- nances of various relative widths as a function of their mass. The puted in the asymptotic approximation to account for the trial observed limits for pole masses ranging from 250 to 750 GeV are factors due to scanning the signal mass hypothesis [52]. Upper obtained with a spacing of 1 GeV. The granularity is reduced above limits at the 95% confidence level (CL) are set on the fiducial cross- that mass, but remains below the experimental resolution of the section times branching ratio into the corresponding dilepton final ee channel. The observed limit on the fiducial cross-section times state, given the integrated luminosity of the data and the signal branching ratio ranges from 3.6 (13.1) fb at 250 GeV to about 0.014 efficiency. The limits are evaluated with the modified frequentist (0.018) fb at 6 TeV for the zero (10%) relative width signal in the CLS method [53] using the asymptotic approximation to the test- statistic distribution [50]. Cross-checks with sampling distributions combined dilepton channel. The impact of systematic uncertainties generated using pseudo-experiments are used to test the accuracy of this approximation for the high-mass part of the dilepton spec- 3 The resulting fit parameters for dielectron channel are: a = 178000 ± 400, b = tra. The approximation is found to lead to limits that are stronger 1.5 ± 1.0, p 0 = −12.38 ± 0.09, p 1 = −4.295 ± 0.014, p 2 = −0.9191 ± 0.0027, p 3 = than those obtained with pseudo-experiments above 3 TeV. This ef- −0.0845 ± 0.0005; for dimuon channel are: a = 138700 ± 400, b = 11.8 ± 0.5, p 0 = fect reaches 25% (35%) at 5 TeV (6 TeV) for the combined dilepton −7.38 ± 0.12, p 1 = −4.132 ± 0.017, p 2 = −1.0637 ± 0.0029, p 3 = −0.1022 ± 0.0005. The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 73 Table 3 Observed and expected 95% CL lower limits on m Z  for three Z  gauge boson models, quoted to the nearest 100 GeV in the ee and μμ channels as well as their combination (). Model Lower limits on m Z  [TeV] ee μμ  obs exp obs exp obs exp  Zψ 4.1 4.3 4.0 4.0 4.5 4.5  Zχ 4.6 4.6 4.2 4.2 4.8 4.8  Z SSM 4.9 4.9 4.5 4.5 5.1 5.1 (g f ≡ g  = gq ) it only exceeds 10% in regions (| g f | > 0.9 and | gh | > 2.5) well outside the limit contours. The observed limits can be compared with the limits obtained for the combination of the  and ν channels in Ref. [39] (provided in brackets): for Fig. 2. Probability that the observed spectrum is compatible with the background- gh = 0 and m Z  = 3 TeV, 4 TeV and 5 TeV the | g f | values above only hypothesis for the dielectron, dimuon and combined dilepton channels. The HVT local p 0 is quantified in standard deviations σ as a function of pole mass m X . 0.07 (0.06), 0.23 (0.15) and 0.49 (0.42) are excluded at 95% CL, re- spectively. The resulting dilepton-only limits are slightly weaker than those for the  and ν channels combined, even with a on this search is small across all mass and width assumptions, re-  four times larger dataset, because of the higher W HVT → ν cross- sulting in the expected limits on the fiducial cross-section times section in this model. branching ratio to dileptons being (4–7)% weaker than those with- A complete set of tables and figures (including additional re- out systematic uncertainties. As all studied signal spin hypotheses sults for the dielectron and dimuon channels) are available at the (0, 1, 2) have efficiency values which are consistent within 4%, Durham HepData repository [55]. the limits shown above can be used for reinterpretation of models with such new resonances. 9. Conclusions The generic cross-section limits at /m = 0.5%, 1.2% and 3.0% are compared with the model predictions of Z ψ  , Z  and Z  χ SSM , re- The ATLAS detector at LHC is used to search for new resonances spectively, to obtain mass limits. The cross-section values for the with mass larger than 250 GeV decaying into a pair of electrons model predictions are obtained in the fiducial volume, for compat- or muons in 139√ fb−1 of proton–proton collision data at a centre- ibility with the definition of the generic signal model. Mass limits of-mass energy s = 13 TeV. A functional form is fitted to the are calculated as the intersection between the expected and ob- dilepton invariant-mass distribution in data events to model the served limits with the model prediction. Table 3 lists the mass contribution from background processes. A generic signal shape is limits for the three tested models in all three channels. These ex- used to determine the significance of observed deviations from the ceed previously reported results [11] by 500–800 GeV. background estimate. No significant deviation is observed. Limits The generic cross-section limits shown in Fig. 3 are smoothly are set on the fiducial cross-section times branching ratio to dielec- interpolated via Delaunay triangulation [54] to produce limits in trons and dimuons for generic resonances with a relative natural between the tested widths. The results are converted into ex- width in the range of zero to 10%. These limits are shown to be clusion contours in the HVT model coupling space presented in applicable to spin-0, spin-1 and spin-2 signal hypotheses. Limits Fig. 4, where g  , gq and gh correspond to the coupling strengths on the Heavy Vector Triplet model couplings and on the masses between the triplet field and the lepton, quark and Higgs and of vector resonances are inferred. In particular, the results imply a vector-boson fields, respectively. In the tested { gq , g  } plane the  (Z lower limit of 4.5 (5.1) TeV on m Z  for the Z ψ SSM ) boson at 95% relative width always remains below 10%, and in the { gh , g f } plane confidence level. These are the most stringent limits to date. Fig. 3. Upper limits at 95% CL on the fiducial cross-section times branching ratio as a function of pole mass for (a) the zero-width, 3%, 10% and (b) 0.5%, 1.2%, 6% relative width signals for the combined dilepton channel. Observed limits are shown as a solid line and expected limits as a dotted/dashed line. Also shown are theoretical cross-sections  for (a) Z SSM ( /m = 3.0%) and (b) Z χ ( /m = 1.2%) and Z  ( /m = 0.5%) in the fiducial region. The signal theoretical uncertainties are shown as a band on the Z  ψ SSM theory line and are derived as in Ref. [11]. 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Bruni 23b , G. Bruni 23b , L.S. Bruni 120 , S. Bruno 73a,73b , B.H. Brunt 32 , M. Bruschi 23b , N. Bruscino 139 , P. Bryant 37 , L. Bryngemark 96 , T. Buanes 17 , Q. Buat 36 , P. Buchholz 151 , A.G. Buckley 57 , I.A. Budagov 79 , M.K. Bugge 134 , F. Bührer 52 , O. Bulekov 112 , T.J. Burch 121 , S. Burdin 90 , C.D. Burgard 120 , A.M. Burger 129 , B. Burghgrave 8 , K. Burka 84 , J.T.P. Burr 46 , V. Büscher 99 , E. Buschmann 53 , P.J. Bussey 57 , J.M. Butler 25 , C.M. Buttar 57 , J.M. Butterworth 94 , P. Butti 36 , W. Buttinger 36 , A. Buzatu 158 , A.R. Buzykaev 122b,122a , G. Cabras 23b,23a , S. Cabrera Urbán 174 , D. Caforio 56 , H. Cai 173 , V.M.M. Cairo 153 , O. Cakir 4a , N. Calace 36 , P. Calafiura 18 , A. Calandri 101 , G. Calderini 136 , P. Calfayan 65 , G. Callea 57 , L.P. Caloba 80b , S. Calvente Lopez 98 , D. Calvet 38 , S. Calvet 38 , T.P. Calvet 155 , M. Calvetti 71a,71b , R. Camacho Toro 136 , S. Camarda 36 , D. Camarero Munoz 98 , P. Camarri 73a,73b , D. Cameron 134 , R. Caminal Armadans 102 , C. Camincher 36 , S. Campana 36 , M. Campanelli 94 , A. Camplani 40 , A. Campoverde 151 , V. Canale 69a,69b , A. Canesse 103 , M. Cano Bret 60c , J. Cantero 129 , T. Cao 161 , Y. Cao 173 , M.D.M. Capeans Garrido 36 , M. Capua 41b,41a , R. Cardarelli 73a , F.C. Cardillo 149 , I. Carli 143 , T. Carli 36 , G. Carlino 69a , B.T. Carlson 139 , L. Carminati 68a,68b , R.M.D. Carney 45a,45b , S. Caron 119 , E. Carquin 147b , S. Carrá 68a,68b , J.W.S. Carter 167 , M.P. Casado 14,e , A.F. Casha 167 , D.W. Casper 171 , R. Castelijn 120 , F.L. Castillo 174 , V. Castillo Gimenez 174 , N.F. Castro 140a,140e , A. Catinaccio 36 , J.R. Catmore 134 , A. Cattai 36 , J. Caudron 24 , V. Cavaliere 29 , E. Cavallaro 14 , D. Cavalli 68a , M. Cavalli-Sforza 14 , V. Cavasinni 71a,71b , E. Celebi 12b , F. Ceradini 74a,74b , L. Cerda Alberich 174 , K. Cerny 130 , A.S. Cerqueira 80a , A. Cerri 156 , L. Cerrito 73a,73b , F. Cerutti 18 , A. Cervelli 23b,23a , S.A. Cetin 12b , D. 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Cinca 47 , V. Cindro 91 , I.A. Cioară 27b , A. Ciocio 18 , F. Cirotto 69a,69b , Z.H. Citron 180 , M. Citterio 68a , D.A. Ciubotaru 27b , B.M. Ciungu 167 , A. Clark 54 , M.R. Clark 39 , P.J. Clark 50 , C. Clement 45a,45b , Y. Coadou 101 , M. Cobal 66a,66c , A. Coccaro 55b , J. Cochran 78 , H. Cohen 161 , A.E.C. Coimbra 36 , L. Colasurdo 119 , B. Cole 39 , A.P. Colijn 120 , J. Collot 58 , P. Conde Muiño 140a,f , E. Coniavitis 52 , S.H. Connell 33b , I.A. Connelly 57 , S. Constantinescu 27b , F. Conventi 69a,ay , A.M. Cooper-Sarkar 135 , F. Cormier 175 , K.J.R. Cormier 167 , L.D. Corpe 94 , M. Corradi 72a,72b , E.E. Corrigan 96 , F. Corriveau 103,ad , A. Cortes-Gonzalez 36 , M.J. Costa 174 , F. Costanza 5 , D. Costanzo 149 , G. Cowan 93 , J.W. Cowley 32 , J. Crane 100 , K. Cranmer 124 , S.J. Crawley 57 , R.A. Creager 137 , S. Crépé-Renaudin 58 , F. Crescioli 136 , M. Cristinziani 24 , V. Croft 120 , G. Crosetti 41b,41a , A. Cueto 5 , T. Cuhadar Donszelmann 149 , A.R. Cukierman 153 , S. Czekierda 84 , P. Czodrowski 36 , M.J. Da Cunha Sargedas De Sousa 60b , J.V. Da Fonseca Pinto 80b , C. Da Via 100 , W. Dabrowski 83a , T. Dado 28a , S. Dahbi 35e , T. Dai 105 , C. Dallapiccola 102 , M. Dam 40 , G. D’amen 23b,23a , V. D’Amico 74a,74b , J. Damp 99 , J.R. Dandoy 137 , M.F. Daneri 30 , N.P. Dang 181 , N.D Dann 100 , M. Danninger 175 , V. Dao 36 , G. Darbo 55b , O. Dartsi 5 , A. Dattagupta 131 , T. Daubney 46 , S. D’Auria 68a,68b , W. Davey 24 , C. David 46 , T. Davidek 143 , D.R. Davis 49 , E. Dawe 104 , I. Dawson 149 , K. De 8 , R. De Asmundis 69a , M. De Beurs 120 , S. De Castro 23b,23a , S. De Cecco 72a,72b , N. De Groot 119 , P. de Jong 120 , H. De la Torre 106 , A. De Maria 15c , D. De Pedis 72a , A. De Salvo 72a , U. De Sanctis 73a,73b , M. De Santis 73a,73b , A. De Santo 156 , K. De Vasconcelos Corga 101 , J.B. De Vivie De Regie 132 , C. Debenedetti 146 , D.V. Dedovich 79 , A.M. Deiana 42 , M. Del Gaudio 41b,41a , J. Del Peso 98 , Y. Delabat Diaz 46 , D. Delgove 132 , F. Deliot 145,q , C.M. Delitzsch 7 , M. Della Pietra 69a,69b , D. Della Volpe 54 , A. Dell’Acqua 36 , L. Dell’Asta 73a,73b , M. Delmastro 5 , C. Delporte 132 , P.A. Delsart 58 , D.A. DeMarco 167 , S. Demers 183 , M. Demichev 79 , G. Demontigny 109 , S.P. Denisov 123 , D. Denysiuk 120 , L. D’Eramo 136 , D. Derendarz 84 , J.E. Derkaoui 35d , F. Derue 136 , P. Dervan 90 , K. Desch 24 , C. Deterre 46 , K. Dette 167 , C. Deutsch 24 , M.R. Devesa 30 , P.O. Deviveiros 36 , A. Dewhurst 144 , S. Dhaliwal 26 , F.A. Di Bello 54 , A. Di Ciaccio 73a,73b , L. Di Ciaccio 5 , W.K. Di Clemente 137 , C. Di Donato 69a,69b , A. Di Girolamo 36 , G. Di Gregorio 71a,71b , B. Di Micco 74a,74b , R. Di Nardo 102 , K.F. Di Petrillo 59 , R. Di Sipio 167 , D. Di Valentino 34 , C. Diaconu 101 , F.A. Dias 40 , T. Dias Do Vale 140a , M.A. Diaz 147a , J. Dickinson 18 , E.B. Diehl 105 , J. Dietrich 19 , S. Díez Cornell 46 , A. Dimitrievska 18 , W. Ding 15b , J. Dingfelder 24 , F. Dittus 36 , F. Djama 101 , T. Djobava 159b , J.I. Djuvsland 17 , M.A.B. Do Vale 80c , M. Dobre 27b , D. Dodsworth 26 , C. Doglioni 96 , J. Dolejsi 143 , Z. Dolezal 143 , M. Donadelli 80d , J. Donini 38 , A. D’onofrio 92 , M. D’Onofrio 90 , J. Dopke 144 , A. Doria 69a , M.T. Dova 88 , A.T. Doyle 57 , E. Drechsler 152 , E. Dreyer 152 , T. Dreyer 53 , A.S. Drobac 170 , Y. Duan 60b , F. Dubinin 110 , M. Dubovsky 28a , A. Dubreuil 54 , E. Duchovni 180 , G. Duckeck 114 , A. Ducourthial 136 , O.A. Ducu 109 , D. Duda 115 , A. Dudarev 36 , A.C. Dudder 99 , E.M. Duffield 18 , L. Duflot 132 , M. Dührssen 36 , C. Dülsen 182 , M. Dumancic 180 , A.E. Dumitriu 27b , A.K. Duncan 57 , M. Dunford 61a , A. Duperrin 101 , H. Duran Yildiz 4a , M. Düren 56 , A. Durglishvili 159b , D. Duschinger 48 , B. Dutta 46 , D. Duvnjak 1 , G.I. Dyckes 137 , M. Dyndal 36 , S. Dysch 100 , B.S. Dziedzic 84 , K.M. Ecker 115 , R.C. Edgar 105 , T. Eifert 36 , G. Eigen 17 , K. Einsweiler 18 , T. Ekelof 172 , M. El Kacimi 35c , R. 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Feng 36 , M. Feng 49 , M.J. Fenton 57 , A.B. Fenyuk 123 , J. Ferrando 46 , A. Ferrante 173 , A. Ferrari 172 , P. Ferrari 120 , R. Ferrari 70a , D.E. Ferreira de Lima 61b , A. Ferrer 174 , D. Ferrere 54 , C. Ferretti 105 , F. Fiedler 99 , A. Filipčič 91 , 78 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 F. Filthaut 119 , K.D. Finelli 25 , M.C.N. Fiolhais 140a , L. Fiorini 174 , F. Fischer 114 , W.C. Fisher 106 , I. Fleck 151 , P. Fleischmann 105 , R.R.M. Fletcher 137 , T. Flick 182 , B.M. Flierl 114 , L.F. Flores 137 , L.R. Flores Castillo 63a , F.M. Follega 75a,75b , N. Fomin 17 , J.H. Foo 167 , G.T. Forcolin 75a,75b , A. Formica 145 , F.A. Förster 14 , A.C. Forti 100 , A.G. Foster 21 , M.G. Foti 135 , D. Fournier 132 , H. Fox 89 , P. Francavilla 71a,71b , S. Francescato 72a,72b , M. Franchini 23b,23a , S. Franchino 61a , D. Francis 36 , L. Franconi 20 , M. Franklin 59 , A.N. Fray 92 , B. Freund 109 , W.S. Freund 80b , E.M. Freundlich 47 , D.C. Frizzell 128 , D. Froidevaux 36 , J.A. Frost 135 , C. Fukunaga 164 , E. Fullana Torregrosa 174 , E. Fumagalli 55b,55a , T. Fusayasu 116 , J. Fuster 174 , A. Gabrielli 23b,23a , A. Gabrielli 18 , G.P. Gach 83a , S. Gadatsch 54 , P. Gadow 115 , G. Gagliardi 55b,55a , L.G. Gagnon 109 , C. Galea 27b , B. Galhardo 140a , G.E. Gallardo 135 , E.J. Gallas 135 , B.J. Gallop 144 , P. Gallus 142 , G. Galster 40 , R. Gamboa Goni 92 , K.K. Gan 126 , S. Ganguly 180 , J. Gao 60a , Y. Gao 90 , Y.S. Gao 31,l , C. García 174 , J.E. García Navarro 174 , J.A. García Pascual 15a , C. Garcia-Argos 52 , M. Garcia-Sciveres 18 , R.W. Gardner 37 , N. Garelli 153 , S. Gargiulo 52 , V. Garonne 134 , A. Gaudiello 55b,55a , G. Gaudio 70a , I.L. Gavrilenko 110 , A. Gavrilyuk 111 , C. Gay 175 , G. Gaycken 24 , E.N. Gazis 10 , A.A. Geanta 27b , C.N.P. Gee 144 , J. Geisen 53 , M. Geisen 99 , M.P. Geisler 61a , C. Gemme 55b , M.H. Genest 58 , C. Geng 105 , S. Gentile 72a,72b , S. George 93 , T. Geralis 44 , D. Gerbaudo 14 , L.O. Gerlach 53 , P. Gessinger-Befurt 99 , G. Gessner 47 , S. Ghasemi 151 , M. Ghasemi Bostanabad 176 , M. Ghneimat 24 , A. Ghosh 77 , B. Giacobbe 23b , S. Giagu 72a,72b , N. Giangiacomi 23b,23a , P. Giannetti 71a , A. Giannini 69a,69b , S.M. Gibson 93 , M. Gignac 146 , D. Gillberg 34 , G. Gilles 182 , D.M. Gingrich 3,ax , M.P. Giordani 66a,66c , F.M. Giorgi 23b , P.F. Giraud 145 , G. Giugliarelli 66a,66c , D. Giugni 68a , F. Giuli 73a,73b , S. Gkaitatzis 162 , I. Gkialas 9,h , E.L. Gkougkousis 14 , P. Gkountoumis 10 , L.K. Gladilin 113 , C. Glasman 98 , J. Glatzer 14 , P.C.F. Glaysher 46 , A. Glazov 46 , M. Goblirsch-Kolb 26 , S. Goldfarb 104 , T. Golling 54 , D. Golubkov 123 , A. Gomes 140a,140b , R. Goncalves Gama 53 , R. Gonçalo 140a,140b , G. Gonella 52 , L. Gonella 21 , A. Gongadze 79 , F. Gonnella 21 , J.L. Gonski 59 , S. González de la Hoz 174 , S. Gonzalez-Sevilla 54 , G.R. Gonzalvo Rodriguez 174 , L. Goossens 36 , P.A. Gorbounov 111 , H.A. Gordon 29 , B. Gorini 36 , E. 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Hod 180 , M.C. Hodgkinson 149 , A. Hoecker 36 , F. Hoenig 114 , D. Hohn 52 , D. Hohov 132 , T.R. Holmes 37 , M. Holzbock 114 , L.B.A.H Hommels 32 , S. Honda 169 , T. Honda 81 , T.M. Hong 139 , The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 79 A. Hönle 115 , B.H. Hooberman 173 , W.H. Hopkins 6 , Y. Horii 117 , P. Horn 48 , A.J. Horton 152 , L.A. Horyn 37 , J-Y. Hostachy 58 , A. Hostiuc 148 , S. Hou 158 , A. Hoummada 35a , J. Howarth 100 , J. Hoya 88 , M. Hrabovsky 130 , J. Hrdinka 76 , I. Hristova 19 , J. Hrivnac 132 , A. Hrynevich 108 , T. Hryn’ova 5 , P.J. Hsu 64 , S.-C. Hsu 148 , Q. Hu 29 , S. Hu 60c , Y. Huang 15a , Z. Hubacek 142 , F. Hubaut 101 , M. Huebner 24 , F. Huegging 24 , T.B. Huffman 135 , M. Huhtinen 36 , R.F.H. Hunter 34 , P. Huo 155 , A.M. Hupe 34 , N. Huseynov 79,af , J. Huston 106 , J. Huth 59 , R. Hyneman 105 , S. Hyrych 28a , G. Iacobucci 54 , G. Iakovidis 29 , I. Ibragimov 151 , L. Iconomidou-Fayard 132 , Z. Idrissi 35e , P.I. Iengo 36 , R. 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Jimenez Pena 174 , S. Jin 15c , A. Jinaru 27b , O. Jinnouchi 165 , H. Jivan 33c , P. Johansson 149 , K.A. Johns 7 , C.A. Johnson 65 , K. Jon-And 45a,45b , R.W.L. Jones 89 , S.D. Jones 156 , S. Jones 7 , T.J. Jones 90 , J. Jongmanns 61a , P.M. Jorge 140a , J. Jovicevic 36 , X. Ju 18 , J.J. Junggeburth 115 , A. Juste Rozas 14,x , A. Kaczmarska 84 , M. Kado 72a,72b , H. Kagan 126 , M. Kagan 153 , C. Kahra 99 , T. Kaji 179 , E. Kajomovitz 160 , C.W. Kalderon 96 , A. Kaluza 99 , A. Kamenshchikov 123 , L. Kanjir 91 , Y. Kano 163 , V.A. Kantserov 112 , J. Kanzaki 81 , L.S. Kaplan 181 , D. Kar 33c , M.J. Kareem 168b , E. Karentzos 10 , S.N. Karpov 79 , Z.M. Karpova 79 , V. Kartvelishvili 89 , A.N. Karyukhin 123 , L. Kashif 181 , R.D. Kass 126 , A. Kastanas 45a,45b , Y. Kataoka 163 , C. Kato 60d,60c , J. Katzy 46 , K. Kawade 82 , K. Kawagoe 87 , T. Kawaguchi 117 , T. Kawamoto 163 , G. Kawamura 53 , E.F. Kay 176 , V.F. Kazanin 122b,122a , R. Keeler 176 , R. Kehoe 42 , J.S. Keller 34 , E. Kellermann 96 , D. Kelsey 156 , J.J. Kempster 21 , J. Kendrick 21 , O. Kepka 141 , S. Kersten 182 , B.P. Kerševan 91 , S. Ketabchi Haghighat 167 , M. Khader 173 , F. Khalil-Zada 13 , M. Khandoga 145 , A. Khanov 129 , A.G. Kharlamov 122b,122a , T. Kharlamova 122b,122a , E.E. Khoda 175 , A. Khodinov 166 , T.J. Khoo 54 , E. Khramov 79 , J. Khubua 159b , S. Kido 82 , M. Kiehn 54 , C.R. Kilby 93 , Y.K. Kim 37 , N. Kimura 66a,66c , O.M. Kind 19 , B.T. King 90,∗ , D. Kirchmeier 48 , J. Kirk 144 , A.E. Kiryunin 115 , T. Kishimoto 163 , D.P. Kisliuk 167 , V. Kitali 46 , O. Kivernyk 5 , E. Kladiva 28b,∗ , T. Klapdor-Kleingrothaus 52 , M.H. Klein 105 , M. Klein 90 , U. Klein 90 , K. Kleinknecht 99 , P. Klimek 121 , A. Klimentov 29 , T. Klingl 24 , T. Klioutchnikova 36 , F.F. Klitzner 114 , P. Kluit 120 , S. Kluth 115 , E. Kneringer 76 , E.B.F.G. Knoops 101 , A. Knue 52 , D. Kobayashi 87 , T. Kobayashi 163 , M. Kobel 48 , M. Kocian 153 , P. Kodys 143 , P.T. Koenig 24 , T. Koffas 34 , N.M. Köhler 115 , T. Koi 153 , M. Kolb 61b , I. Koletsou 5 , T. Komarek 130 , T. Kondo 81 , N. Kondrashova 60c , K. Köneke 52 , A.C. König 119 , T. Kono 125 , R. Konoplich 124,an , V. Konstantinides 94 , N. Konstantinidis 94 , B. Konya 96 , R. Kopeliansky 65 , S. Koperny 83a , K. Korcyl 84 , K. Kordas 162 , G. Koren 161 , A. Korn 94 , I. Korolkov 14 , E.V. Korolkova 149 , N. Korotkova 113 , O. Kortner 115 , S. Kortner 115 , T. Kosek 143 , V.V. Kostyukhin 24 , A. Kotwal 49 , A. Koulouris 10 , A. Kourkoumeli-Charalampidi 70a,70b , C. Kourkoumelis 9 , E. Kourlitis 149 , V. Kouskoura 29 , A.B. Kowalewska 84 , R. Kowalewski 176 , C. Kozakai 163 , W. Kozanecki 145 , A.S. Kozhin 123 , V.A. Kramarenko 113 , G. Kramberger 91 , D. Krasnopevtsev 60a , M.W. Krasny 136 , A. Krasznahorkay 36 , D. Krauss 115 , J.A. Kremer 83a , J. Kretzschmar 90 , P. Krieger 167 , F. Krieter 114 , A. Krishnan 61b , K. Krizka 18 , K. Kroeninger 47 , H. Kroha 115 , J. Kroll 141 , J. Kroll 137 , J. Krstic 16 , U. Kruchonak 79 , H. Krüger 24 , N. Krumnack 78 , M.C. Kruse 49 , J.A. Krzysiak 84 , T. Kubota 104 , S. Kuday 4b , J.T. Kuechler 46 , S. Kuehn 36 , A. Kugel 61a , T. Kuhl 46 , V. Kukhtin 79 , R. Kukla 101 , Y. Kulchitsky 107,aj , S. Kuleshov 147b , Y.P. Kulinich 173 , M. Kuna 58 , T. Kunigo 85 , A. Kupco 141 , T. Kupfer 47 , O. Kuprash 52 , H. Kurashige 82 , L.L. Kurchaninov 168a , Y.A. Kurochkin 107 , A. Kurova 112 , M.G. Kurth 15a,15d , E.S. Kuwertz 36 , M. Kuze 165 , A.K. Kvam 148 , J. Kvita 130 , T. Kwan 103 , A. La Rosa 115 , L. La Rotonda 41b,41a , F. La Ruffa 41b,41a , C. Lacasta 174 , F. Lacava 72a,72b , D.P.J. Lack 100 , H. Lacker 19 , D. Lacour 136 , E. Ladygin 79 , R. Lafaye 5 , B. Laforge 136 , T. Lagouri 33c , S. Lai 53 , S. Lammers 65 , W. Lampl 7 , C. Lampoudis 162 , E. Lançon 29 , U. Landgraf 52 , M.P.J. Landon 92 , M.C. Lanfermann 54 , V.S. Lang 46 , J.C. Lange 53 , R.J. Langenberg 36 , A.J. Lankford 171 , F. Lanni 29 , K. Lantzsch 24 , A. Lanza 70a , A. Lapertosa 55b,55a , S. Laplace 136 , J.F. Laporte 145 , T. Lari 68a , F. Lasagni Manghi 23b,23a , M. Lassnig 36 , T.S. Lau 63a , A. Laudrain 132 , A. Laurier 34 , M. Lavorgna 69a,69b , M. Lazzaroni 68a,68b , B. Le 104 , O. Le Dortz 136 , E. Le Guirriec 101 , M. LeBlanc 7 , 80 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 T. LeCompte 6 , F. Ledroit-Guillon 58 , C.A. Lee 29 , G.R. Lee 17 , L. Lee 59 , S.C. Lee 158 , S.J. Lee 34 , B. Lefebvre 168a , M. Lefebvre 176 , F. Legger 114 , C. Leggett 18 , K. Lehmann 152 , N. Lehmann 182 , G. Lehmann Miotto 36 , W.A. Leight 46 , A. Leisos 162,w , M.A.L. Leite 80d , R. Leitner 143 , D. Lellouch 180,∗ , K.J.C. Leney 42 , T. Lenz 24 , B. Lenzi 36 , R. Leone 7 , S. Leone 71a , C. Leonidopoulos 50 , A. Leopold 136 , G. Lerner 156 , C. Leroy 109 , R. Les 167 , C.G. Lester 32 , M. Levchenko 138 , J. Levêque 5 , D. Levin 105 , L.J. Levinson 180 , D.J. Lewis 21 , B. Li 15b , B. Li 105 , C-Q. Li 60a , F. Li 60c , H. Li 60a , H. Li 60b , J. 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Lösle 52 , X. Lou 46 , X. Lou 15a , A. Lounis 132 , J. Love 6 , P.A. Love 89 , J.J. Lozano Bahilo 174 , M. Lu 60a , Y.J. Lu 64 , H.J. Lubatti 148 , C. Luci 72a,72b , A. Lucotte 58 , C. Luedtke 52 , F. Luehring 65 , I. Luise 136 , L. Luminari 72a , B. Lund-Jensen 154 , M.S. Lutz 102 , D. Lynn 29 , R. Lysak 141 , E. Lytken 96 , F. Lyu 15a , V. Lyubushkin 79 , T. Lyubushkina 79 , H. Ma 29 , L.L. Ma 60b , Y. Ma 60b , G. Maccarrone 51 , A. Macchiolo 115 , C.M. Macdonald 149 , J. Machado Miguens 137 , D. Madaffari 174 , R. Madar 38 , W.F. Mader 48 , N. Madysa 48 , J. Maeda 82 , K. Maekawa 163 , S. Maeland 17 , T. Maeno 29 , M. Maerker 48 , A.S. Maevskiy 113 , V. Magerl 52 , N. Magini 78 , D.J. Mahon 39 , C. Maidantchik 80b , T. Maier 114 , A. Maio 140a,140b,140d , O. Majersky 28a , S. Majewski 131 , Y. Makida 81 , N. Makovec 132 , B. Malaescu 136 , Pa. Malecki 84 , V.P. Maleev 138 , F. Malek 58 , U. Mallik 77 , D. Malon 6 , C. Malone 32 , S. Maltezos 10 , S. Malyukov 36 , J. 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Maxfield 90 , D.A. Maximov 122b,122a , R. Mazini 158 , I. Maznas 162 , S.M. Mazza 146 , S.P. Mc Kee 105 , T.G. McCarthy 115 , L.I. McClymont 94 , W.P. McCormack 18 , E.F. McDonald 104 , J.A. Mcfayden 36 , M.A. McKay 42 , K.D. McLean 176 , S.J. McMahon 144 , P.C. McNamara 104 , C.J. McNicol 178 , R.A. McPherson 176,ad , J.E. Mdhluli 33c , Z.A. Meadows 102 , S. Meehan 148 , T. Megy 52 , S. Mehlhase 114 , A. Mehta 90 , T. Meideck 58 , B. Meirose 43 , D. Melini 174 , B.R. Mellado Garcia 33c , J.D. Mellenthin 53 , M. Melo 28a , F. Meloni 46 , A. Melzer 24 , S.B. Menary 100 , E.D. Mendes Gouveia 140a,140e , L. Meng 36 , X.T. Meng 105 , S. Menke 115 , E. Meoni 41b,41a , S. Mergelmeyer 19 , S.A.M. Merkt 139 , C. Merlassino 20 , P. Mermod 54 , L. Merola 69a,69b , C. Meroni 68a , O. Meshkov 113,110 , J.K.R. Meshreki 151 , A. Messina 72a,72b , J. Metcalfe 6 , A.S. Mete 171 , C. Meyer 65 , J. Meyer 160 , J-P. Meyer 145 , H. Meyer Zu Theenhausen 61a , F. Miano 156 , R.P. Middleton 144 , L. Mijović 50 , G. Mikenberg 180 , M. Mikestikova 141 , M. Mikuž 91 , H. Mildner 149 , M. Milesi 104 , A. Milic 167 , D.A. Millar 92 , D.W. Miller 37 , A. Milov 180 , D.A. Milstead 45a,45b , R.A. Mina 153,p , A.A. Minaenko 123 , M. Miñano Moya 174 , I.A. Minashvili 159b , A.I. Mincer 124 , B. Mindur 83a , M. Mineev 79 , Y. Minegishi 163 , Y. Ming 181 , L.M. Mir 14 , A. Mirto 67a,67b , K.P. Mistry 137 , T. Mitani 179 , J. Mitrevski 114 , V.A. Mitsou 174 , M. Mittal 60c , A. Miucci 20 , P.S. Miyagawa 149 , A. Mizukami 81 , J.U. Mjörnmark 96 , T. Mkrtchyan 184 , M. Mlynarikova 143 , T. Moa 45a,45b , K. Mochizuki 109 , P. Mogg 52 , S. Mohapatra 39 , R. Moles-Valls 24 , M.C. Mondragon 106 , K. Mönig 46 , J. Monk 40 , E. Monnier 101 , A. Montalbano 152 , J. Montejo Berlingen 36 , M. Montella 94 , F. Monticelli 88 , S. Monzani 68a , N. Morange 132 , D. Moreno 22 , M. Moreno Llácer 36 , C. Moreno Martinez 14 , P. Morettini 55b , M. Morgenstern 120 , S. Morgenstern 48 , D. Mori 152 , M. Morii 59 , M. Morinaga 179 , V. Morisbak 134 , A.K. Morley 36 , G. Mornacchi 36 , A.P. Morris 94 , L. Morvaj 155 , P. Moschovakos 36 , B. Moser 120 , M. Mosidze 159b , T. Moskalets 145 , H.J. Moss 149 , J. Moss 31,m , The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 81 K. Motohashi 165 , E. Mountricha 36 , E.J.W. Moyse 102 , S. Muanza 101 , J. Mueller 139 , R.S.P. Mueller 114 , D. Muenstermann 89 , G.A. Mullier 96 , J.L. Munoz Martinez 14 , F.J. Munoz Sanchez 100 , P. Murin 28b , W.J. Murray 178,144 , A. Murrone 68a,68b , M. Muškinja 18 , C. Mwewa 33a , A.G. Myagkov 123,ao , J. Myers 131 , M. Myska 142 , B.P. Nachman 18 , O. Nackenhorst 47 , A. Nag Nag 48 , K. Nagai 135 , K. Nagano 81 , Y. Nagasaka 62 , M. Nagel 52 , E. Nagy 101 , A.M. Nairz 36 , Y. Nakahama 117 , K. Nakamura 81 , T. Nakamura 163 , I. Nakano 127 , H. Nanjo 133 , F. Napolitano 61a , R.F. Naranjo Garcia 46 , R. Narayan 11 , D.I. Narrias Villar 61a , I. Naryshkin 138 , T. Naumann 46 , G. Navarro 22 , H.A. Neal 105,∗ , P.Y. Nechaeva 110 , F. Nechansky 46 , T.J. Neep 21 , A. Negri 70a,70b , M. Negrini 23b , C. Nellist 53 , M.E. Nelson 135 , S. Nemecek 141 , P. Nemethy 124 , M. Nessi 36,d , M.S. Neubauer 173 , M. Neumann 182 , P.R. Newman 21 , T.Y. Ng 63c , Y.S. Ng 19 , Y.W.Y. Ng 171 , H.D.N. Nguyen 101 , T. Nguyen Manh 109 , E. Nibigira 38 , R.B. Nickerson 135 , R. Nicolaidou 145 , D.S. Nielsen 40 , J. Nielsen 146 , N. Nikiforou 11 , V. Nikolaenko 123,ao , I. Nikolic-Audit 136 , K. Nikolopoulos 21 , P. Nilsson 29 , H.R. Nindhito 54 , Y. Ninomiya 81 , A. Nisati 72a , N. Nishu 60c , R. Nisius 115 , I. Nitsche 47 , T. Nitta 179 , T. Nobe 163 , Y. Noguchi 85 , I. Nomidis 136 , M.A. Nomura 29 , M. Nordberg 36 , N. Norjoharuddeen 135 , T. Novak 91 , O. Novgorodova 48 , R. Novotny 142 , L. Nozka 130 , K. Ntekas 171 , E. Nurse 94 , F.G. Oakham 34,ax , H. Oberlack 115 , J. Ocariz 136 , A. Ochi 82 , I. Ochoa 39 , J.P. Ochoa-Ricoux 147a , K. O’Connor 26 , S. Oda 87 , S. Odaka 81 , S. Oerdek 53 , A. Ogrodnik 83a , A. Oh 100 , S.H. Oh 49 , C.C. Ohm 154 , H. Oide 55b,55a , M.L. Ojeda 167 , H. Okawa 169 , Y. Okazaki 85 , Y. Okumura 163 , T. Okuyama 81 , A. Olariu 27b , L.F. Oleiro Seabra 140a , S.A. Olivares Pino 147a , D. Oliveira Damazio 29 , J.L. Oliver 1 , M.J.R. Olsson 171 , A. Olszewski 84 , J. Olszowska 84 , D.C. O’Neil 152 , A. Onofre 140a,140e , K. Onogi 117 , P.U.E. Onyisi 11 , H. Oppen 134 , M.J. Oreglia 37 , G.E. Orellana 88 , Y. Oren 161 , D. Orestano 74a,74b , N. Orlando 14 , R.S. Orr 167 , V. O’Shea 57 , R. Ospanov 60a , G. Otero y Garzon 30 , H. Otono 87 , M. Ouchrif 35d , F. Ould-Saada 134 , A. Ouraou 145 , Q. Ouyang 15a , M. Owen 57 , R.E. Owen 21 , V.E. Ozcan 12c , N. Ozturk 8 , J. Pacalt 130 , H.A. Pacey 32 , K. Pachal 49 , A. Pacheco Pages 14 , C. Padilla Aranda 14 , S. Pagan Griso 18 , M. Paganini 183 , G. Palacino 65 , S. Palazzo 50 , S. Palestini 36 , M. Palka 83b , D. Pallin 38 , I. Panagoulias 10 , C.E. Pandini 36 , J.G. Panduro Vazquez 93 , P. Pani 46 , G. Panizzo 66a,66c , L. Paolozzi 54 , C. Papadatos 109 , K. Papageorgiou 9,h , A. Paramonov 6 , D. Paredes Hernandez 63b , S.R. Paredes Saenz 135 , B. Parida 166 , T.H. Park 167 , A.J. Parker 89 , M.A. Parker 32 , F. Parodi 55b,55a , E.W.P. Parrish 121 , J.A. Parsons 39 , U. Parzefall 52 , L. Pascual Dominguez 136 , V.R. Pascuzzi 167 , J.M.P. Pasner 146 , E. Pasqualucci 72a , S. Passaggio 55b , F. Pastore 93 , P. Pasuwan 45a,45b , S. Pataraia 99 , J.R. Pater 100 , A. Pathak 181 , T. Pauly 36 , B. Pearson 115 , M. Pedersen 134 , L. Pedraza Diaz 119 , R. Pedro 140a , T. Peiffer 53 , S.V. Peleganchuk 122b,122a , O. Penc 141 , H. Peng 60a , B.S. Peralva 80a , M.M. Perego 132 , A.P. Pereira Peixoto 140a , D.V. Perepelitsa 29 , F. Peri 19 , L. Perini 68a,68b , H. Pernegger 36 , S. Perrella 69a,69b , K. Peters 46 , R.F.Y. Peters 100 , B.A. Petersen 36 , T.C. Petersen 40 , E. Petit 101 , A. Petridis 1 , C. Petridou 162 , P. Petroff 132 , M. Petrov 135 , F. Petrucci 74a,74b , M. Pettee 183 , N.E. Pettersson 102 , K. Petukhova 143 , A. Peyaud 145 , R. Pezoa 147b , L. Pezzotti 70a,70b , T. Pham 104 , F.H. Phillips 106 , P.W. Phillips 144 , M.W. Phipps 173 , G. Piacquadio 155 , E. Pianori 18 , A. Picazio 102 , R.H. Pickles 100 , R. Piegaia 30 , D. Pietreanu 27b , J.E. Pilcher 37 , A.D. Pilkington 100 , M. Pinamonti 73a,73b , J.L. Pinfold 3 , M. Pitt 180 , L. Pizzimento 73a,73b , M.-A. Pleier 29 , V. Pleskot 143 , E. Plotnikova 79 , D. Pluth 78 , P. Podberezko 122b,122a , R. Poettgen 96 , R. Poggi 54 , L. Poggioli 132 , I. Pogrebnyak 106 , D. Pohl 24 , I. Pokharel 53 , G. Polesello 70a , A. Poley 18 , A. Policicchio 72a,72b , R. Polifka 143 , A. Polini 23b , C.S. Pollard 46 , V. Polychronakos 29 , D. Ponomarenko 112 , L. Pontecorvo 36 , S. Popa 27a , G.A. Popeneciu 27d , D.M. Portillo Quintero 58 , S. Pospisil 142 , K. Potamianos 46 , I.N. Potrap 79 , C.J. Potter 32 , H. Potti 11 , T. Poulsen 96 , J. Poveda 36 , T.D. Powell 149 , G. Pownall 46 , M.E. Pozo Astigarraga 36 , P. Pralavorio 101 , S. Prell 78 , D. Price 100 , M. Primavera 67a , S. Prince 103 , M.L. Proffitt 148 , N. Proklova 112 , K. Prokofiev 63c , F. Prokoshin 79 , S. Protopopescu 29 , J. Proudfoot 6 , M. Przybycien 83a , D. Pudzha 138 , A. Puri 173 , P. Puzo 132 , J. Qian 105 , Y. Qin 100 , A. Quadt 53 , M. Queitsch-Maitland 46 , A. Qureshi 1 , P. Rados 104 , F. Ragusa 68a,68b , G. Rahal 97 , J.A. Raine 54 , S. Rajagopalan 29 , A. Ramirez Morales 92 , K. Ran 15a,15d , T. Rashid 132 , S. Raspopov 5 , M.G. Ratti 68a,68b , D.M. Rauch 46 , F. Rauscher 114 , S. Rave 99 , B. Ravina 149 , I. Ravinovich 180 , J.H. Rawling 100 , M. Raymond 36 , A.L. Read 134 , N.P. Readioff 58 , M. Reale 67a,67b , D.M. Rebuzzi 70a,70b , A. Redelbach 177 , G. Redlinger 29 , K. Reeves 43 , L. Rehnisch 19 , J. Reichert 137 , D. Reikher 161 , A. Reiss 99 , A. Rej 151 , C. Rembser 36 , M. Renda 27b , M. Rescigno 72a , S. Resconi 68a , E.D. Resseguie 137 , S. Rettie 175 , E. Reynolds 21 , O.L. Rezanova 122b,122a , P. Reznicek 143 , E. Ricci 75a,75b , R. Richter 115 , S. Richter 46 , E. Richter-Was 83b , O. Ricken 24 , M. Ridel 136 , P. Rieck 115 , 82 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 C.J. Riegel 182 , O. Rifki 46 , M. Rijssenbeek 155 , A. Rimoldi 70a,70b , M. Rimoldi 20 , L. Rinaldi 23b , G. Ripellino 154 , B. Ristić 89 , E. Ritsch 36 , I. Riu 14 , J.C. Rivera Vergara 147a , F. Rizatdinova 129 , E. Rizvi 92 , C. Rizzi 36 , R.T. Roberts 100 , S.H. Robertson 103,ad , M. Robin 46 , D. Robinson 32 , J.E.M. Robinson 46 , A. Robson 57 , E. Rocco 99 , C. Roda 71a,71b , S. Rodriguez Bosca 174 , A. Rodriguez Perez 14 , D. Rodriguez Rodriguez 174 , A.M. Rodríguez Vera 168b , S. Roe 36 , O. Røhne 134 , R. Röhrig 115 , C.P.A. Roland 65 , J. Roloff 59 , A. Romaniouk 112 , M. Romano 23b,23a , N. Rompotis 90 , M. Ronzani 124 , L. Roos 136 , S. Rosati 72a , K. Rosbach 52 , N-A. Rosien 53 , G. Rosin 102 , B.J. Rosser 137 , E. Rossi 46 , E. Rossi 74a,74b , E. Rossi 69a,69b , L.P. Rossi 55b , L. Rossini 68a,68b , R. Rosten 14 , M. Rotaru 27b , J. Rothberg 148 , D. Rousseau 132 , G. Rovelli 70a,70b , D. Roy 33c , A. Rozanov 101 , Y. Rozen 160 , X. Ruan 33c , F. Rubbo 153 , F. Rühr 52 , A. Ruiz-Martinez 174 , A. Rummler 36 , Z. Rurikova 52 , N.A. Rusakovich 79 , H.L. Russell 103 , L. Rustige 38,47 , J.P. Rutherfoord 7 , E.M. Rüttinger 46,j , Y.F. Ryabov 138 , M. Rybar 39 , G. Rybkin 132 , A. Ryzhov 123 , G.F. Rzehorz 53 , P. Sabatini 53 , G. Sabato 120 , S. Sacerdoti 132 , H.F-W. Sadrozinski 146 , R. Sadykov 79 , F. Safai Tehrani 72a , B. Safarzadeh Samani 156 , P. Saha 121 , S. Saha 103 , M. Sahinsoy 61a , A. Sahu 182 , M. Saimpert 46 , M. Saito 163 , T. Saito 163 , H. Sakamoto 163 , A. Sakharov 124,an , D. Salamani 54 , G. Salamanna 74a,74b , J.E. Salazar Loyola 147b , P.H. Sales De Bruin 172 , D. Salihagic 115,∗ , A. Salnikov 153 , J. Salt 174 , D. Salvatore 41b,41a , F. Salvatore 156 , A. Salvucci 63a,63b,63c , A. Salzburger 36 , J. Samarati 36 , D. Sammel 52 , D. Sampsonidis 162 , D. Sampsonidou 162 , J. Sánchez 174 , A. Sanchez Pineda 66a,66c , H. Sandaker 134 , C.O. Sander 46 , I.G. Sanderswood 89 , M. Sandhoff 182 , C. Sandoval 22 , D.P.C. Sankey 144 , M. Sannino 55b,55a , Y. Sano 117 , A. Sansoni 51 , C. Santoni 38 , H. Santos 140a,140b , S.N. Santpur 18 , A. Santra 174 , A. Sapronov 79 , J.G. Saraiva 140a,140d , O. Sasaki 81 , K. Sato 169 , E. Sauvan 5 , P. Savard 167,ax , N. Savic 115 , R. Sawada 163 , C. Sawyer 144 , L. Sawyer 95,al , C. Sbarra 23b , A. Sbrizzi 23a , T. Scanlon 94 , J. Schaarschmidt 148 , P. Schacht 115 , B.M. Schachtner 114 , D. Schaefer 37 , L. Schaefer 137 , J. Schaeffer 99 , S. Schaepe 36 , U. Schäfer 99 , A.C. Schaffer 132 , D. Schaile 114 , R.D. Schamberger 155 , N. Scharmberg 100 , V.A. Schegelsky 138 , D. Scheirich 143 , F. Schenck 19 , M. Schernau 171 , C. Schiavi 55b,55a , S. Schier 146 , L.K. Schildgen 24 , Z.M. Schillaci 26 , E.J. Schioppa 36 , M. Schioppa 41b,41a , K.E. Schleicher 52 , S. Schlenker 36 , K.R. Schmidt-Sommerfeld 115 , K. Schmieden 36 , C. Schmitt 99 , S. Schmitt 46 , S. Schmitz 99 , J.C. Schmoeckel 46 , U. Schnoor 52 , L. Schoeffel 145 , A. Schoening 61b , P.G. Scholer 52 , E. Schopf 135 , M. Schott 99 , J.F.P. Schouwenberg 119 , J. Schovancova 36 , S. Schramm 54 , F. Schroeder 182 , A. Schulte 99 , H-C. Schultz-Coulon 61a , M. Schumacher 52 , B.A. Schumm 146 , Ph. Schune 145 , A. Schwartzman 153 , T.A. Schwarz 105 , Ph. Schwemling 145 , R. Schwienhorst 106 , A. Sciandra 146 , G. Sciolla 26 , M. Scodeggio 46 , M. Scornajenghi 41b,41a , F. Scuri 71a , F. Scutti 104 , L.M. Scyboz 115 , C.D. Sebastiani 72a,72b , P. Seema 19 , S.C. Seidel 118 , A. Seiden 146 , T. Seiss 37 , J.M. Seixas 80b , G. Sekhniaidze 69a , K. Sekhon 105 , S.J. Sekula 42 , N. Semprini-Cesari 23b,23a , S. Sen 49 , S. Senkin 38 , C. Serfon 76 , L. Serin 132 , L. Serkin 66a,66b , M. Sessa 60a , H. Severini 128 , F. Sforza 170 , A. Sfyrla 54 , E. Shabalina 53 , J.D. Shahinian 146 , N.W. Shaikh 45a,45b , D. Shaked Renous 180 , L.Y. Shan 15a , R. Shang 173 , J.T. Shank 25 , M. Shapiro 18 , A. Sharma 135 , A.S. Sharma 1 , P.B. Shatalov 111 , K. Shaw 156 , S.M. Shaw 100 , A. Shcherbakova 138 , Y. Shen 128 , N. Sherafati 34 , A.D. Sherman 25 , P. Sherwood 94 , L. Shi 158,at , S. Shimizu 81 , C.O. Shimmin 183 , Y. Shimogama 179 , M. Shimojima 116 , I.P.J. Shipsey 135 , S. Shirabe 87 , M. Shiyakova 79,aa , J. Shlomi 180 , A. Shmeleva 110 , M.J. Shochet 37 , S. Shojaii 104 , D.R. Shope 128 , S. Shrestha 126 , E. Shulga 180 , P. Sicho 141 , A.M. Sickles 173 , P.E. Sidebo 154 , E. Sideras Haddad 33c , O. Sidiropoulou 36 , A. Sidoti 23b,23a , F. Siegert 48 , Dj. Sijacki 16 , M. Silva Jr. 181 , M.V. Silva Oliveira 80a , S.B. Silverstein 45a , S. Simion 132 , E. Simioni 99 , R. Simoniello 99 , P. Sinervo 167 , N.B. Sinev 131 , M. Sioli 23b,23a , I. Siral 105 , S.Yu. Sivoklokov 113 , J. Sjölin 45a,45b , E. Skorda 96 , P. Skubic 128 , M. Slawinska 84 , K. Sliwa 170 , R. Slovak 143 , V. Smakhtin 180 , B.H. Smart 144 , J. Smiesko 28a , N. Smirnov 112 , S.Yu. Smirnov 112 , Y. Smirnov 112 , L.N. Smirnova 113,t , O. Smirnova 96 , J.W. Smith 53 , M. Smizanska 89 , K. Smolek 142 , A. Smykiewicz 84 , A.A. Snesarev 110 , H.L. Snoek 120 , I.M. Snyder 131 , S. Snyder 29 , R. Sobie 176,ad , A.M. Soffa 171 , A. Soffer 161 , A. Søgaard 50 , F. Sohns 53 , C.A. Solans Sanchez 36 , E.Yu. Soldatov 112 , U. Soldevila 174 , A.A. Solodkov 123 , A. Soloshenko 79 , O.V. Solovyanov 123 , V. Solovyev 138 , P. Sommer 149 , H. Son 170 , W. Song 144 , W.Y. Song 168b , A. Sopczak 142 , F. Sopkova 28b , C.L. Sotiropoulou 71a,71b , S. Sottocornola 70a,70b , R. Soualah 66a,66c,g , A.M. Soukharev 122b,122a , D. South 46 , S. Spagnolo 67a,67b , M. Spalla 115 , M. Spangenberg 178 , F. Spanò 93 , D. Sperlich 52 , T.M. Spieker 61a , R. Spighi 23b , G. Spigo 36 , M. Spina 156 , D.P. Spiteri 57 , M. Spousta 143 , A. Stabile 68a,68b , B.L. Stamas 121 , R. Stamen 61a , M. Stamenkovic 120 , E. Stanecka 84 , R.W. Stanek 6 , B. Stanislaus 135 , M.M. Stanitzki 46 , The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 83 M. Stankaityte 135 , B. Stapf 120 , E.A. Starchenko 123 , G.H. Stark 146 , J. Stark 58 , S.H Stark 40 , P. Staroba 141 , P. Starovoitov 61a , S. Stärz 103 , R. Staszewski 84 , G. Stavropoulos 44 , M. Stegler 46 , P. Steinberg 29 , A.L. Steinhebel 131 , B. Stelzer 152 , H.J. Stelzer 139 , O. Stelzer-Chilton 168a , H. Stenzel 56 , T.J. Stevenson 156 , G.A. Stewart 36 , M.C. Stockton 36 , G. Stoicea 27b , M. Stolarski 140a , P. Stolte 53 , S. Stonjek 115 , A. Straessner 48 , J. Strandberg 154 , S. Strandberg 45a,45b , M. Strauss 128 , P. Strizenec 28b , R. Ströhmer 177 , D.M. Strom 131 , R. Stroynowski 42 , A. Strubig 50 , S.A. Stucci 29 , B. Stugu 17 , J. Stupak 128 , N.A. Styles 46 , D. Su 153 , S. Suchek 61a , V.V. Sulin 110 , M.J. Sullivan 90 , D.M.S. Sultan 54 , S. Sultansoy 4c , T. Sumida 85 , S. Sun 105 , X. Sun 3 , K. Suruliz 156 , C.J.E. Suster 157 , M.R. Sutton 156 , S. Suzuki 81 , M. Svatos 141 , M. Swiatlowski 37 , S.P. Swift 2 , T. Swirski 177 , A. Sydorenko 99 , I. Sykora 28a , M. Sykora 143 , T. Sykora 143 , D. Ta 99 , K. Tackmann 46,y , J. Taenzer 161 , A. Taffard 171 , R. Tafirout 168a , E. Tahirovic 92 , H. Takai 29 , R. Takashima 86 , K. Takeda 82 , T. Takeshita 150 , E.P. Takeva 50 , Y. Takubo 81 , M. Talby 101 , A.A. Talyshev 122b,122a , N.M. Tamir 161 , J. Tanaka 163 , M. Tanaka 165 , R. Tanaka 132 , B.B. Tannenwald 126 , S. Tapia Araya 173 , S. Tapprogge 99 , A. Tarek Abouelfadl Mohamed 136 , S. Tarem 160 , G. Tarna 27b,c , G.F. Tartarelli 68a , P. Tas 143 , M. Tasevsky 141 , T. Tashiro 85 , E. Tassi 41b,41a , A. Tavares Delgado 140a,140b , Y. Tayalati 35e , A.J. Taylor 50 , G.N. Taylor 104 , W. Taylor 168b , A.S. Tee 89 , R. Teixeira De Lima 153 , P. Teixeira-Dias 93 , H. Ten Kate 36 , J.J. Teoh 120 , S. Terada 81 , K. Terashi 163 , J. Terron 98 , S. Terzo 14 , M. Testa 51 , R.J. Teuscher 167,ad , S.J. Thais 183 , T. Theveneaux-Pelzer 46 , F. Thiele 40 , D.W. Thomas 93 , J.O. Thomas 42 , J.P. Thomas 21 , A.S. Thompson 57 , P.D. Thompson 21 , L.A. Thomsen 183 , E. Thomson 137 , Y. Tian 39 , R.E. Ticse Torres 53 , V.O. Tikhomirov 110,ap , Yu.A. Tikhonov 122b,122a , S. Timoshenko 112 , P. Tipton 183 , S. Tisserant 101 , K. Todome 23b,23a , S. Todorova-Nova 5 , S. Todt 48 , J. Tojo 87 , S. Tokár 28a , K. Tokushuku 81 , E. Tolley 126 , K.G. Tomiwa 33c , M. Tomoto 117 , L. Tompkins 153,p , K. Toms 118 , B. Tong 59 , P. Tornambe 102 , E. Torrence 131 , H. Torres 48 , E. Torró Pastor 148 , C. Tosciri 135 , J. Toth 101,ab , D.R. Tovey 149 , C.J. Treado 124 , T. Trefzger 177 , F. Tresoldi 156 , A. Tricoli 29 , I.M. Trigger 168a , S. Trincaz-Duvoid 136 , W. Trischuk 167 , B. Trocmé 58 , A. Trofymov 132 , C. Troncon 68a , M. Trovatelli 176 , F. Trovato 156 , L. Truong 33b , M. Trzebinski 84 , A. Trzupek 84 , F. Tsai 46 , J.C-L. Tseng 135 , P.V. Tsiareshka 107,aj , A. Tsirigotis 162 , N. Tsirintanis 9 , V. Tsiskaridze 155 , E.G. Tskhadadze 159a , M. Tsopoulou 162 , I.I. Tsukerman 111 , V. Tsulaia 18 , S. Tsuno 81 , D. Tsybychev 155 , Y. Tu 63b , A. Tudorache 27b , V. Tudorache 27b , T.T. Tulbure 27a , A.N. Tuna 59 , S. Turchikhin 79 , D. Turgeman 180 , I. Turk Cakir 4b,u , R.J. Turner 21 , R.T. Turra 68a , P.M. Tuts 39 , S Tzamarias 162 , E. Tzovara 99 , G. Ucchielli 47 , K. Uchida 163 , I. Ueda 81 , M. Ughetto 45a,45b , F. Ukegawa 169 , G. Unal 36 , A. Undrus 29 , G. Unel 171 , F.C. Ungaro 104 , Y. Unno 81 , K. Uno 163 , J. Urban 28b , P. Urquijo 104 , G. Usai 8 , J. Usui 81 , L. Vacavant 101 , V. Vacek 142 , B. Vachon 103 , K.O.H. Vadla 134 , A. Vaidya 94 , C. Valderanis 114 , E. Valdes Santurio 45a,45b , M. Valente 54 , S. Valentinetti 23b,23a , A. Valero 174 , L. Valéry 46 , R.A. Vallance 21 , A. Vallier 36 , J.A. Valls Ferrer 174 , T.R. Van Daalen 14 , P. Van Gemmeren 6 , I. Van Vulpen 120 , M. Vanadia 73a,73b , W. Vandelli 36 , A. Vaniachine 166 , D. Vannicola 72a,72b , R. Vari 72a , E.W. Varnes 7 , C. Varni 55b,55a , T. Varol 42 , D. Varouchas 132 , K.E. Varvell 157 , M.E. Vasile 27b , G.A. Vasquez 176 , J.G. Vasquez 183 , F. Vazeille 38 , D. Vazquez Furelos 14 , T. Vazquez Schroeder 36 , J. Veatch 53 , V. Vecchio 74a,74b , M.J. Veen 120 , L.M. Veloce 167 , F. Veloso 140a,140c , S. Veneziano 72a , A. Ventura 67a,67b , N. Venturi 36 , A. Verbytskyi 115 , V. Vercesi 70a , M. Verducci 74a,74b , C.M. Vergel Infante 78 , C. Vergis 24 , W. Verkerke 120 , A.T. Vermeulen 120 , J.C. Vermeulen 120 , M.C. Vetterli 152,ax , N. Viaux Maira 147b , M. Vicente Barreto Pinto 54 , T. Vickey 149 , O.E. Vickey Boeriu 149 , G.H.A. Viehhauser 135 , L. Vigani 135 , M. Villa 23b,23a , M. Villaplana Perez 68a,68b , E. Vilucchi 51 , M.G. Vincter 34 , V.B. Vinogradov 79 , A. Vishwakarma 46 , C. Vittori 23b,23a , I. Vivarelli 156 , M. Vogel 182 , P. Vokac 142 , S.E. von Buddenbrock 33c , E. Von Toerne 24 , V. Vorobel 143 , K. Vorobev 112 , M. Vos 174 , J.H. Vossebeld 90 , M. Vozak 100 , N. Vranjes 16 , M. Vranjes Milosavljevic 16 , V. Vrba 142 , M. Vreeswijk 120 , T. Šfiligoj 91 , R. Vuillermet 36 , I. Vukotic 37 , T. Ženiš 28a , L. Živković 16 , P. Wagner 24 , W. Wagner 182 , J. Wagner-Kuhr 114 , H. Wahlberg 88 , K. Wakamiya 82 , V.M. Walbrecht 115 , J. Walder 89 , R. Walker 114 , S.D. Walker 93 , W. Walkowiak 151 , V. Wallangen 45a,45b , A.M. Wang 59 , C. Wang 60b , F. Wang 181 , H. Wang 18 , H. Wang 3 , J. Wang 157 , J. Wang 61b , P. Wang 42 , Q. Wang 128 , R.-J. Wang 99 , R. Wang 60a , R. Wang 6 , S.M. Wang 158 , W.T. Wang 60a , W. Wang 15c,ae , W.X. Wang 60a,ae , Y. Wang 60a,am , Z. Wang 60c , C. Wanotayaroj 46 , A. Warburton 103 , C.P. Ward 32 , D.R. Wardrope 94 , N. Warrack 57 , A. Washbrook 50 , A.T. Watson 21 , M.F. Watson 21 , G. Watts 148 , B.M. Waugh 94 , A.F. Webb 11 , S. Webb 99 , C. Weber 183 , M.S. Weber 20 , S.A. Weber 34 , S.M. Weber 61a , A.R. Weidberg 135 , J. Weingarten 47 , 84 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 M. Weirich 99 , C. Weiser 52 , P.S. Wells 36 , T. Wenaus 29 , T. Wengler 36 , S. Wenig 36 , N. Wermes 24 , M.D. Werner 78 , P. Werner 36 , M. Wessels 61a , T.D. Weston 20 , K. Whalen 131 , N.L. Whallon 148 , A.M. Wharton 89 , A.S. White 105 , A. White 8 , M.J. White 1 , D. Whiteson 171 , B.W. Whitmore 89 , F.J. Wickens 144 , W. Wiedenmann 181 , M. Wielers 144 , N. Wieseotte 99 , C. Wiglesworth 40 , L.A.M. Wiik-Fuchs 52 , F. Wilk 100 , H.G. Wilkens 36 , L.J. Wilkins 93 , H.H. Williams 137 , S. Williams 32 , C. Willis 106 , S. Willocq 102 , J.A. Wilson 21 , I. Wingerter-Seez 5 , E. Winkels 156 , F. Winklmeier 131 , O.J. Winston 156 , B.T. Winter 52 , M. Wittgen 153 , M. Wobisch 95 , A. Wolf 99 , T.M.H. Wolf 120 , R. Wolff 101 , R.W. Wölker 135 , J. Wollrath 52 , M.W. Wolter 84 , H. Wolters 140a,140c , V.W.S. Wong 175 , N.L. Woods 146 , S.D. Worm 21 , B.K. Wosiek 84 , K.W. Woźniak 84 , K. Wraight 57 , S.L. 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Zwalinski 36 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 Física d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Barcelona, Spain 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 23 (a) INFN Bologna and Università 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 Física, 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 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 85 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 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 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 Física, 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 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 Física 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 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 Física 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 86 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 107 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 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 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 Física Experimental de Partículas – LIP; (b) Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Lisboa; (c) Departamento de Física, Universidade de Coimbra, Coimbra; (d) Centro de Física Nuclear da Universidade de Lisboa, Lisboa; (e) Departamento de Física, Universidade do Minho, Braga; (f ) Universidad de Granada, Granada (Spain); (g) Dep Física 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 Física, Pontificia Universidad Católica de Chile, Santiago; (b) Departamento de Física, Universidad Técnica Federico Santa María, Valparaíso, 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 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 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 Física 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 The ATLAS Collaboration / Physics Letters B 796 (2019) 68–87 87 184 Yerevan Physics Institute, Yerevan, Armenia a Also at Centre for High Performance Computing, CSIR Campus, Rosebank, Cape Town; South Africa. b Also at CERN, Geneva; Switzerland. c Also at CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille; France. d Also at Département de Physique Nucléaire et Corpusculaire, Université de Genève, Genève; Switzerland. e Also at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona; Spain. f Also at Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Lisboa; Portugal. g Also at Department of Applied Physics and Astronomy, University of Sharjah, Sharjah; United Arab Emirates. h Also at Department of Financial and Management Engineering, University of the Aegean, Chios; Greece. i Also at Department of Physics and Astronomy, University of Louisville, Louisville, KY; United States of America. j Also at Department of Physics and Astronomy, University of Sheffield, Sheffield; United Kingdom. k Also at Department of Physics, California State University, East Bay; United States of America. l Also at Department of Physics, California State University, Fresno; United States of America. m Also at Department of Physics, California State University, Sacramento; United States of America. n Also at Department of Physics, King’s College London, London; United Kingdom. o Also at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg; Russia. p Also at Department of Physics, Stanford University, Stanford CA; United States of America. q Also at Department of Physics, University of Adelaide, Adelaide; Australia. 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 Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona; Spain. y Also at Institut für Experimentalphysik, Universität Hamburg, Hamburg; Germany. z Also at Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen; Netherlands. aa Also at Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia; Bulgaria. ab Also at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest; Hungary. ac Also at Institute of High Energy Physics, Chinese Academy of Sciences, Beijing; China. 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 Physics Dept, University of South Africa, Pretoria; South Africa. as Also at Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg; Germany. at Also at School of Physics, Sun Yat-sen University, Guangzhou; China. au Also at The City College of New York, New York NY; United States of America. av Also at The Collaborative Innovation Center of Quantum Matter (CICQM), Beijing; China. aw Also at Tomsk State University, Tomsk, and Moscow Institute of Physics and Technology State University, Dolgoprudny; Russia. ax Also at TRIUMF, Vancouver BC; Canada. ay Also at Universita di Napoli Parthenope, Napoli; Italy. ∗ Deceased.