PHYSICAL REVIEW D 99, 072009 (2019) Measurement of thepffiffitt̄Z and tt̄W cross sections in proton-proton collisions at s = 13 TeV with the ATLAS detector M. Aaboud et al.* (ATLAS Collaboration) (Received 14 January 2019; published 29 April 2019) A measurement of the associated production of a top-quark pair (tt̄) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb−1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The tt̄Z and tt̄W production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σ tt̄Z ¼ 0.95  0.08stat  0.10syst pb and σ tt̄W ¼ 0.87  0.13stat  0.14syst pb in agreement with the Standard Model predictions. The measurement of the tt̄Z cross section is used to set constraints on effective field theory operators which modify the tt̄Z vertex. DOI: 10.1103/PhysRevD.99.072009 I. INTRODUCTION SMEFT context. The tt̄Z and tt̄W processes were observed by ATLAS [15,16] and CMS [17,18], with measured cross Properties of the top quark have been explored by the sections compatible with the SM prediction. At 13 TeV, Large Hadron Collider (LHC) and previous collider experi- ATLAS analyzed 3.2 fb−1 of data using the same-sign ments in great detail. The production cross sections of top- dimuon, trilepton and tetralepton channels, and mea- quark pairs and single top quarks, as well as the top-quark sured σ tt̄Z ¼ 0.9  0.3 pb and σ tt̄W ¼ 1.5  0.8 pb, while mass, spin correlations and W boson helicity fractions have CMS analyzed 35.9 fb−1 and measured 0.99þ0.15 −0.13 pb and all been measured. Other properties of the top quark are now becoming accessible, owing to the large center- 0.77þ0.18 −0.16 pb, respectively. of-mass energy and luminosity at the LHC. These include The production of tt̄Z and tt̄W is often an important its coupling to the Higgs boson and electroweak neutral- background in searches involving final states with multiple current couplings, accessed by measurements of pair- leptons and b-quarks. These processes also constitute an produced top quarks in association with a Higgs boson important background in measurements of the associated [1–4] or a photon [5–8]. production of the Higgs boson with top quarks. Measurements of top-quark pairs in association with a Z This paper presents measurements of the tt̄Z and tt̄W or W boson (tt̄Z and tt̄W) provide a direct probe of the cross sections using proton-proton pffiffiffi (pp) collision data at a weak couplings of the top quark [9–11]. These couplings center-of mass energy s ¼ 13 TeV corresponding to an may be modified in the presence of physics beyond the integrated luminosity of 36.1 fb−1 , collected by the ATLAS Standard Model (BSM). Any deviations from the SM detector in 2015 and 2016. The final states of top-quark predictions due to BSM effects can be parametrized in a pairs produced in association with a Z or a W boson contain model-independent way using the framework of the up to four isolated, prompt leptons.1 In this analysis, events Standard Model effective field theory (SMEFT) [12–14]. with two opposite-sign (OS) or same-sign (SS) leptons, three leptons or four leptons are considered. The dominant If no deviations are observed, measurements of the tt̄Z and backgrounds in these four channels are Z þ jets and tt̄, tt̄W production cross sections, σ tt̄Z and σ tt̄W , can be used to events with nonprompt or misidentified leptons, WZ, and set constraints on the weak couplings of the top quark in the ZZ production, respectively. An interpretation of the tt̄Z cross-section measurement in the SMEFT framework is * Full author list given at the end of the article. also performed. Published by the American Physical Society under the terms of 1 the Creative Commons Attribution 4.0 International license. In this paper, lepton is used to denote electron or muon, and Further distribution of this work must maintain attribution to prompt lepton is used to denote a lepton produced in a Z or W the author(s) and the published article’s title, journal citation, boson decay, or in the decay of a τ-lepton which arises from a Z and DOI. Funded by SCOAP3. or W boson decay. 2470-0010=2019=99(7)=072009(38) 072009-1 © 2019 CERN, for the ATLAS Collaboration M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) II. THE ATLAS DETECTOR described below. In all samples the top-quark mass was set to 172.5 GeV, and the Higgs boson mass was set to The ATLAS detector [19] consists of three main sub- 125 GeV. The response of the detector to stable3 particles systems: an inner tracking system, electromagnetic (EM) was emulated by a dedicated simulation [27] based either and hadronic calorimeters, and a muon spectrometer (MS). fully on GEANT [28], or on a faster simulation [29] using a The inner detector (ID) consists of a high-granularity parametrized calorimeter response and GEANT for other silicon pixel detector, including the insertable B-layer detector systems. To account for additional pp interactions [20,21], which is the innermost layer of the tracking from the same and nearby bunch crossings (pileup), system, and a silicon microstrip tracker, together providing minimum-bias interactions generated using PYTHIA precision tracking in the pseudorapidity2 range jηj < 2.5, v8.186 [30], referred to as PYTHIA 8 in the following, followed by a transition radiation tracker covering with the A2 [31] set of tuned MC parameters (A2 tune) jηj < 2.0. All these systems are immersed in a 2 T magnetic were superimposed on the hard-scattering events. field provided by a thin superconducting solenoid. The EM Simulated events were corrected using per-event weights sampling calorimeter uses lead and liquid argon (LAr) and to describe the distribution of the average number of is divided into barrel (jηj < 1.475) and end cap (1.375 < interactions per proton bunch crossing as observed in jηj < 3.2) regions. Hadronic calorimetry is provided by a data. All samples were processed through the same steel/scintillator-tile calorimeter, segmented into three bar- reconstruction software as used for the data. Simulated rel structures, in the range jηj < 1.7, and by two copper/ LAr hadronic end cap calorimeters that cover the region events were corrected so that the object identification, 1.5 < jηj < 3.2. The solid angle coverage is completed reconstruction and trigger efficiencies, energy scales and with forward copper/LAr and tungsten/LAr calorimeter energy resolutions match those determined from data modules, optimized for EM and hadronic measurements, control samples. respectively, covering the region 3.1 < jηj < 4.9. The muon The associated production of a top-quark pair with one or spectrometer measures the deflection of muons in the range two vector bosons was generated at next-to-leading order jηj < 2.7 using multiple layers of high-precision tracking (NLO) with MADGRAPH5_aMC@NLO [32] (referred to in chambers located in toroidal magnetic fields. The field the following as MG5_aMC) version 2.3.2 interfaced to integral of the toroids ranges between 2.0 and 6.0 Tm PYTHIA 8. The cross sections for the tt̄Z and tt̄W processes for most of the detector. The muon spectrometer is also at 13 TeV, computed including NLO QCD and electroweak instrumented with separate trigger chambers covering corrections using MG5_aMC, are σ tt̄Z ¼ 0.88 pb and jηj < 2.4. A two-level trigger system [22], using custom σ tt̄W ¼ 0.60 pb with an uncertainty of ∼12% [32–34]. hardware followed by a software-based trigger level, is The uncertainty is primarily due to higher-order QCD used to reduce the event rate to an average of around 1 kHz corrections, estimated by varying the renormalization (μR ) for offline storage. and factorization (μF ) scales. The γ  contribution and the Z=γ  interference were included in the tt̄Z samples, with the dilepton invariant mass (mll ) required to be above III. DATA AND SIMULATED EVENT SAMPLES 5 GeV. The NNPDF2.3NLO parton distribution function The data were collected with the ATLAS detector during (PDF) set [35] was used in the matrix-element (ME) 2015 and 2016 at a proton-proton (pp) collision energy of computation. The A14 [36] set of tuned MC parameters 13 TeV. The bunch spacing was 25 ns and the mean number (A14 tune) was used together with the NNPDF2.3LO PDF of interactions per bunch crossing was 14 (25) in 2015 set [37] in the parton shower. (2016). With strict data-quality requirements, the integrated The t-channel production of a single top quark in luminosity considered corresponds to 36.1 fb−1 [23,24]. association with a Z boson (tZ) was generated at leading Monte Carlo (MC) simulation samples are used to model order (LO) using MG5_aMC v2.2.3 interfaced to PYTHIA the expected signal and background distributions in the v6.427 [38], referred to as PYTHIA 6 in the following, with different control, validation and signal regions described the CTEQ6L1 [39] PDF set and the Perugia2012 [40] below. The heavy-flavor hadron decays involving b- and set of tuned MC parameters at NLO in QCD. The four- c-quarks, particularly important in this measurement, were flavor scheme was used in the generation, and the sample modeled using EVTGEN [25] v1.2.0, except for those was normalized using the cross section computed at NLO processes modeled using the SHERPA [26] generator, as in QCD using MG5_aMC. The production of a single top quark together with a W 2 ATLAS uses a right-handed coordinate system with its origin and a Z boson (tWZ) was generated with MG5_aMC v2.3.3 at the nominal interaction point (IP) in the center of the detector using the NNPDF3.0NLO PDF set [35]. The generation and the z axis along the beam pipe. The x axis points from the IP was performed at NLO in QCD using the five-flavor to the center of the LHC ring, and the y axis points upward. scheme. Diagrams containing a top-quark pair were Cylindrical coordinates ðr; ϕÞ are used in the transverse plane, ϕ being the azimuthal angle around the z axis. The pseudorapidity is defined in terms of the polar angle θ as η ¼ − ln tanðθ=2Þ. A particle is considered stable if cτ ≥ 1 cm. 3 072009-2 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) removed to avoid overlap with the tt̄Z process. The parton POWHEG-BOX v1, and the parton shower modeled by shower was modeled by PYTHIA 8 with the A14 tune. The PYTHIA v6.428. The CT10 PDF set was used for s-channel sample was normalized using the NLO cross section production and Wt events, while for t-channel production obtained from the generator. the four-flavor scheme was used for the NLO matrix Events containing Z or W bosons with associated jets were element calculations together with the fixed four-flavor simulated using the SHERPA 2.2.1 event generator. The PDF set CT10f4. Diagram removal was employed to matrix-element calculation was performed using COMIX remove the overlap between tt̄ and Wt production [52]. The [41] and OPENLOOPS [42] for up to two partons at NLO single-top-quark samples were normalized to the cross and four partons at LO, and merged with the SHERPA sections computed at NLO reported in Refs. [53,54] for the parton shower [43] according to the ME+PS@NLO pre- s- and t-channels and at NLO with next-to-next-to-leading- scription [44]. The NNPDF3.0NNLO PDF set was used in logarithm soft-gluon corrections for Wt production [55]. conjunction with dedicated parton-shower tuning developed Samples of tt̄ events produced in association with a by the SHERPA authors. The Z=W þ jets samples were Higgs boson (tt̄H) were generated using NLO matrix normalized to next-to-next-to-leading-order (NNLO) QCD elements in MG5_aMC with the NNPDF3.0NLO PDF cross sections for Z=W production calculated by the FEWZ set and interfaced to PYTHIA 8 for the modeling of the program [45]. parton shower. Higgs boson production via gluon-gluon Diboson processes with four charged leptons (4l), three fusion (ggF) and vector-boson fusion (VBF) was generated charged leptons and one neutrino (lllν) or two charged using the POWHEG-BOX v2 generator with the CT10 PDF leptons and two neutrinos (llνν) were simulated using the set. The parton shower and underlying event were SHERPA 2.1.1 generator. The matrix elements included all simulated using PYTHIA 8 with the CTEQ6L1 PDF set diagrams with four electroweak vertices. They were calcu- and AZNLO tune. Higgs boson production with a vector lated including up to three partons at LO, and the CT10 boson was generated at LO using PYTHIA 8 with PDF set [46] was used in conjunction with a dedicated the NNPDF2.3LO PDF. All Higgs boson samples were parton-shower tune developed by the SHERPA authors. The normalized using theoretical calculations presented in invariant mass of any two opposite-sign, same-flavor Ref. [34]. (OSSF) leptons was required to be greater than 5 GeV The SM production of three and four top quarks in the generated events. was generated at LO with MG5_aMC+PYTHIA 8, using The production of three massive vector bosons with the A14 tune together with the NNPDF2.3LO PDF set. The subsequent leptonic decays of all three bosons was mod- samples were normalized using cross sections computed at eled at LO with the SHERPA 2.1.1 generator and the CT10 NLO [56,57]. PDF set. Up to two additional partons were included in the The events with a Z or W boson in association with a matrix element at LO and the full NLO accuracy was used photon were simulated with up to three partons at LO using for the inclusive process. SHERPA 2.1.1 (ME þ PS mode) and the CT10 PDF set. Electroweak processes involving the vector-boson They were normalized to the LO cross section obtained scattering (VBS) diagram and producing two same-sign from the generator. The tt̄γ process was generated at LO leptons, two neutrinos and two partons were modeled with MG5_aMC+PYTHIA 8, using the A14 tune together using SHERPA 2.1.1 at LO accuracy and the CT10 PDF with the NNPDF2.3LO PDF set and normalized to the set. Processes of orders four and six in the electroweak NLO cross section. Events in the tt̄ sample with radiated coupling constant were considered, and up to one addi- photons of high transverse momentum were vetoed to avoid tional parton was included in the matrix element. Other overlap with those from the tt̄γ sample. VBS processes are found to be negligible in the analysis regions considered. IV. OBJECT RECONSTRUCTION The POWHEG-BOX [47–50] v2 generator with the NNPDF3.0NLO PDF set was used for the generation of Electron candidates [58] are reconstructed from tt̄ events. The parton shower and the underlying event were energy deposits (clusters) in the EM calorimeter that are simulated using PYTHIA 8 with the NNPDF2.3LO PDF set associated with reconstructed tracks in the ID. Electrons are and the corresponding A14 tune. The hdamp parameter, required to pass the “medium” likelihood identification which controls the transverse momentum of the first gluon requirements described in Ref. [58]. In the SS dilepton emission beyond the Born configuration, was set to 1.5 channel, the “tight” likelihood requirement is used instead. times the top-quark mass. The tt̄ samples were normalized The electrons are also required to have transverse momen- to the NNLO cross-section predictions, including soft- tum pT > 7 GeV and jηcluster j < 2.47, where ηcluster is the gluon resummation to next-to-next-to-leading-logarithm pseudorapidity of the calorimeter energy deposit associated order, as calculated with the Top++2.0 [51] program. with the electron candidate. Candidates in the EM calo- Electroweak s-channel and t-channel single-top- rimeter barrel/end cap transition region 1.37 < jηcluster j < quark events, and Wt final states, were generated with 1.52 are excluded. 072009-3 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) Muon candidates are reconstructed from a fit to track the efficiency of the discriminant in simulation to that segments in the various layers of the muon spectrometer, measured in data. matched with tracks identified in the inner detector. For both the electrons and muons, the longitudinal Muons are required to have pT > 7 GeV and jηj < 2.5 impact parameter of the associated track relative to the and to pass the medium identification requirements defined primary vertex,4 z0 , is required to satisfy jz0 sinθj < 0.5 mm. in Ref. [59]. The medium criteria include requirements The significance of the transverse impact parameter d0 on the numbers of hits in the ID and MS as well as a is required to satisfy jd0 j=σðd0 Þ < 5 for electrons and compatibility requirement between momentum measure- jd0 j=σðd0 Þ < 3 for muons, where σðd0 Þ is the uncertainty ments in the ID and MS. They provide a high efficiency and in d0 . purity of selected muons. Electron candidates sharing a Jets are reconstructed using the anti-kt algorithm [60,61] track with a muon candidate are removed. with radius parameter R ¼ 0.4, starting from topological To reduce the background due to nonprompt leptons energy clusters in the calorimeters [62]. The effect of from hadron decays, photon conversions or jets misidenti- pileup on jet energies is accounted for by a jet-area-based fied as leptons (labeled as “fake leptons” throughout this correction [63] and the energy resolution of the jets is paper), electron and muon candidates are required to be improved by using global sequential corrections [64]. Jets isolated. In the OS dilepton and the tetralepton channels, are calibrated to the hadronic energy scale using energy- as well as in those trilepton regions that target the tt̄Z and pseudorapidity-dependent calibration factors derived process, the total sum of the track transverse momenta pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi from data. Jets are accepted if they fulfill the requirements in a surrounding cone of size ΔRη ≡ ðΔηÞ þ ðΔϕÞ2 ¼ 2 pT > 25 GeV and jηj < 2.5. To reduce the contribution minð10 GeV=pT ; re;μ Þ, excluding the track of the candi- from jets associated with pileup, jets with pT < 60 GeV date, is required to be less than 6% of the candidate pT , and jηj < 2.4 are required to satisfy pileup rejection criteria where re ¼ 0.2 and rμ ¼ 0.3. In addition, the sum of the (JVT), based on a multivariate combination of track-based cluster transverse energies in the calorimeter within a cone variables [65]. of size ΔRη ¼ 0.2 around any electron candidate, exclud- Jets are tagged as likely to contain b-hadrons (b-tagged) ing energy deposits of the candidate itself, is required to be with a multivariate discriminant making use of the long less than 6% of the candidate pT . lifetime, large decay multiplicity, hard fragmentation and In the SS dilepton channel and those trilepton regions high mass of b-hadrons [66]. For the working point used in targeting the tt̄W process, where the fake-lepton back- this analysis, the average efficiency for correctly tagging a ground is particularly important, tighter isolation require- b-jet is approximately 77%, as determined in simulated tt̄ ments are imposed on candidate leptons. A multivariate events. In simulation, the tagging algorithm gives a discriminant is built to distinguish prompt leptons from rejection factor of 134 against light-quark and gluon jets, leptons arising from heavy-hadron decays inside jets [1]. and 6.2 against charm-quark jets. The b-tagging efficiency The discriminant uses information from charged-particle and mistagging rates in simulation are corrected to repro- tracks in a cone around the lepton candidate. Jets are duce those in data [66]. reconstructed from these tracks to obtain a track jet, and The missing transverse momentum pmiss T , with magni- the discriminant is constructed from information such as tude Emiss T , is a measure of the transverse momentum the angular distance between the lepton and the track imbalance due to particles escaping detection. It is com- jet, the number of tracks in the track jet and the ratio of the puted [67] as the negative sum of the transverse momenta lepton candidate pT to the track-jet pT . The rejection factor of all electrons, muons and jets and an additional soft obtained for leptons from b-hadron decays is about 20, term. The soft term is constructed from all tracks that are while the prompt-lepton efficiency is about 85% (80%) for associated with the primary vertex but not with any lepton pT ∼ 20 GeV and reaches a plateau of ∼98% (96%) for or jet. In this way, the Emiss T is adjusted for the best muons (electrons) at high pT . Simulated events are cor- calibration of the jets and the other identified objects, rected to account for differences in the prompt-lepton while maintaining pileup independence in the soft tagging discriminant between data and simulation. term [67,68]. Another important background in the SS dilepton To prevent double-counting of electron energy deposits channel arises from electrons with misidentified charge. as jets, the closest jet within ΔRy ¼ p0.2 of a reconstructed ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi To suppress this background, another multivariate dis- electron is removed, where ΔRy ≡ ðΔyÞ2 þ ðΔϕÞ2 and y criminant is used, which takes as inputs various track is the rapidity of the electron. If the nearest jet surviving the and cluster properties of the electron candidates [1]. The above criterion is within ΔRy ¼ 0.4 of an electron, the discriminant provides a 95% efficiency for electrons with correct charge reconstruction while achieving a rejection 4 A primary vertex candidate is defined as a vertex with at least factor of ∼17 for electrons with misidentified charge two associated tracks, consistent with the beam collision region. that pass the tight likelihood identification requirement. The vertex candidate with the largest sum of squared transverse Correction factors are applied to selected electrons to match momenta of its associated tracks is taken as the primary vertex. 072009-4 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) electron is discarded to ensure that selected electrons are in pT and η and is found to range from around 0.01% sufficiently separated from nearby jet activity. To reduce to 2%, increasing with pT and η, for electrons passing the the background from muons originating from heavy-flavor identification and isolation criteria applied in the SS particle decays inside jets, muons are removed if they are dilepton channel. The probability is extracted by maximiz- separated from the nearest jet by ΔRy < 0.4. However, if ing a likelihood which relates the number of events in this jet has fewer than three associated tracks, the muon is which the two electrons have the same charge to the total kept and the jet is removed instead; this ensures that high- number of observed events. The background contribution energy muons undergoing significant energy loss in the from events other than charge-flip electrons in the same- calorimeter are retained. sign region is estimated from a sideband of the mll distribution and subtracted before performing the like- V. EVENT SELECTION AND lihood fit. BACKGROUND ESTIMATION The charge-flip background contribution in any SS dilepton region is estimated by constructing a control Table I lists the analysis channels and the targeted decay region with identical requirements, but without any require- modes of the tt̄Z and tt̄W processes. Each channel is ment on the lepton charge, and applying the appropriate divided into multiple analysis regions in order to enhance charge-flip probabilities. the sensitivity to the signal. Simultaneous fits to the signal Background sources involving one or more fake leptons regions and dedicated control regions are performed to are modeled using data events from dedicated regions. For extract the cross sections for tt̄Z and tt̄W production. the SS dilepton (2l-SS) and trilepton channels the fake- Only events collected using single-electron or single- lepton background is estimated using the matrix method muon triggers are accepted. Events are required to have at [69]. The matrix method makes use of events with the same least one reconstructed primary vertex. In all regions selection as the region of interest, but for which the electron considered, at least one reconstructed lepton with pT > identification criteria are relaxed to the “loose” likelihood 27 GeV is required to match (ΔRη < 0.15) a lepton with requirement of Ref. [58], and neither electrons nor muons the same flavor reconstructed by the trigger algorithm. Four are required to be isolated. These leptons are referred to as channels are defined: same-sign dilepton, opposite-sign loose leptons, whereas leptons satisfying the full set of dilepton, trilepton and tetralepton. identification and isolation criteria of Sec. IV are referred The shapes of background distributions containing to as tight leptons. The fake-lepton background in any prompt leptons are modeled by simulation. The normal- region of interest is obtained from the aforementioned izations for the WZ and ZZ processes, as well as the events using efficiencies for prompt and fake leptons to production of a Z boson in association with heavy-flavor satisfy the tight criteria. (HF) jets, are taken from data control regions as defined The lepton efficiencies are extracted in control regions in this section and which are included in the fit discussed with a likelihood fit, by using the model of the matrix in Sec. VII. The yields in these data control regions method, and assuming that the number of events with two are extrapolated to the signal regions using simulation. fake leptons is negligible. The control regions are defined Systematic uncertainties in the extrapolation are taken in dilepton events, separately for events with exactly one into account in the overall uncertainty in the background b-tagged jet and ≥2 b-tagged jets. The prompt lepton estimate. efficiencies are measured in inclusive OSSF events, while The contribution from events containing an electron with fake-lepton efficiencies are measured in events with same- misidentified charge (referred to as “charge-flip” in the sign leptons. Both the prompt and fake-lepton efficiencies following) is estimated from data. The charge-flip proba- are parametrized as a function of the lepton pT . The bility is extracted in events containing a pair of electrons measurement of fake-lepton efficiencies is performed after with mll close to the Z boson mass. It is parametrized subtracting the estimated contribution from charge-flip events. Contributions from processes with two prompt TABLE I. List of tt̄W and tt̄Z decay modes and analysis channels targeting them. The symbols b and ν denote a bottom TABLE II. Summary of the event selection requirements in the quark or antiquark and neutrino or antineutrino, respectively, with OS dilepton signal regions. charge conjugation implied. Variable 2l-Z-6j1b 2l-Z-5j2b 2l-Z-6j2b Process tt̄ decay Boson decay Channel Leptons ¼2, same flavor and opposite sign tt̄W ðl νbÞðqq̄bÞ l ν SS dilepton mll jmll − mZ j < 10 GeV ðl νbÞðl∓ νbÞ l ν Trilepton pT (leading lepton) >30 GeV tt̄Z ðqq̄bÞðqq̄bÞ lþ l− OS dilepton pT (subleading lepton) >15 GeV ðl νbÞðqq̄bÞ lþ l− Trilepton nb-tags 1 ≥2 ≥2 ðl νbÞðl∓ νbÞ lþ l− Tetralepton njets ≥6 5 ≥6 072009-5 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) ATLAS 160 ATLAS 50 s = 13 TeV, 36.1 fb-1 Data tt s = 13 TeV, 36.1 fb-1 Data tt eμ-Z-6j1b-CR 140 eμ-Z-5j2b-CR Other Uncertainty Other Uncertainty 40 120 100 Events / 0.1 Events / 0.1 30 80 20 60 40 10 20 0 0 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 BDT output BDT output (a) (b) ATLAS 80 s = 13 TeV, 36.1 fb-1 Data tt eμ-Z-6j2b-CR 70 Other Uncertainty 60 Events / 0.1 50 40 30 20 10 0 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 BDT output (c) FIG. 1. The BDT distributions for the tt̄ control regions (a) 2l-Z-6j1b, (b) 2l-Z-5j2b, (c) 2l-Z-6j2b. The shaded band represents the total uncertainty. The “Other” background contains SM processes with small cross sections producing two opposite-sign prompt leptons, including the tt̄Z process, whose contribution is negligible. same-sign leptons or one real lepton and a photon con- different lepton isolation requirements applied in the two version (arising mainly from tt̄γ production) are estimated sets of regions. from simulation and are also subtracted. The prompt and In the tetralepton channel, the matrix method is not fake-lepton efficiencies are extracted separately for the used due to the small number of events in data with regions targeting tt̄Z and those targeting tt̄W, due to the four selected leptons. Instead, the contribution from TABLE III. Summary of the event selection requirements in the SS dilepton signal regions. Requirement 2l-SS(p,m)-1b 2e-SS(p,m)-2b eμ-SS(p,m)-2b 2μ-SS(p,m)-2b nb-tags =1 ≥2 ≥2 ≥2 Emiss T >40 GeV >40 GeV >40 GeV >20 GeV HT >240 GeV pT (leading lepton) >27 GeV pT (subleading lepton) >27 GeV njets ≥4 ≥4 ≥4 ≥2 Z veto jmll − mZ j >10 GeV in the 2e and 2μ regions 072009-6 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) backgrounds containing fake leptons is estimated from and trained separately for each region against all the simulation and corrected with scale factors determined in contributing backgrounds, using as input 15, 14 and 17 control regions. The contributions from events containing a variables for 2l-Z-6j1b, 2l-Z-5j2b and 2l-Z-6j2b, respec- photon conversion (denoted by γ þ X) in the SS dilepton tively. Fourteen of the variables are common to the three and trilepton channels are estimated from simulation and regions. The details of the variables used are given in scaled with these correction factors, obtained separately for Table XI in the Appendix. In all three regions, the variables lepton type and origin. with the largest discriminative power are found to be (i) the η of the dilepton system, A. Opposite-sign dilepton analysis (ii) the scalar sum of transverse momenta of all jets divided by the sum of their energies, The OS dilepton analysis targets the tt̄Z process, where (iii) the first Fox-Wolfram moment H1 [70]. both top quarks decay hadronically and the Z boson decays Each of the signal regions is further divided into 19 to a pair of leptons (electrons or muons). Events are equal-size bins of the BDT distribution. To avoid relying on required to have exactly two OSSF leptons. Events with simulation for the normalization of Z þ HF jet production, additional isolated leptons are rejected. The invariant mass the Z þ jets background is constrained by using events with of the lepton pair is required to be in the Z boson mass low values of the BDT discriminant. The simulated Z þ window, jmll − mZ j < 10 GeV. The leading (subleading) jets background is split into three components, Z þ 0HF, lepton is required to have a transverse momentum of at Z þ 1HF and Z þ 2HF, depending on the number of least 30 (15) GeV. reconstructed jets which are matched to a generator-level The OS dilepton analysis is affected by large back- b- or c-hadron (heavy-flavor, or HF jets). The normaliza- grounds from Z þ jets or tt̄ production, both characterized tion factors of the Z þ 1HF and Z þ 2HF components of by the presence of two leptons. In order to improve the the Z þ jets background are determined from the fit to data, signal-to-background ratio and constrain these back- as described in Sec. VII, while the normalization of the grounds from data, three separate analysis regions are Z þ 0HF component is taken from simulation. considered, depending on the number of jets (njets ) and A data-driven method is used to estimate the tt̄ back- number of b-tagged jets (nb-tags ): 2l-Z-5j2b, 2l-Z-6j1b and ground in the OS dilepton signal regions. Control regions 2l-Z-6j2b. The signal region requirements are summarized are defined which are identical to the signal regions, except in Table II. In signal region 2l-Z-5j2b, exactly five jets that the requirement of two leptons with the same flavor are required, of which at least two must be b-tagged. In 2l- and opposite sign is replaced by the requirement Z-6j1b (2l-Z-6j2b), at least six jets are required with of two leptons with different flavors and opposite sign. exactly one (at least two) being b-tagged jets. In this manner, three regions enriched in tt̄ background In order to separate signal from background, boosted are obtained. The number of tt̄ events in each same- decision trees (BDTs) are used. The BDTs are constructed flavor dilepton region is estimated from corresponding 160 140 ATLAS Data ttW ATLAS Data ttW s = 13 TeV, 36.1 fb-1 Other γ +X s = 13 TeV, 36.1 fb-1 Other γ +X 140 2e-SS-1b-VR (pre-fit) 120 2e-SS-1b-VR (pre-fit) Charge-flips Fake Leptons Charge-flips Fake Leptons Uncertainty Uncertainty 120 100 Events / 20 GeV Events / 10 GeV 100 80 80 60 60 40 40 20 20 0 0 20 40 60 80 100 120 140 160 180 200 30 40 50 60 70 80 90 100 110 120 mll [GeV] Leading lepton p [GeV] T (a) (b) FIG. 2. Distributions in the 2e-SS-1b-VR validation region: (a) the invariant mass mll of the lepton pair and (b) leading lepton transverse momentum pT . The shaded band represents the total uncertainty. The “Other” background contains SM processes with small cross sections producing two same-sign prompt leptons. The last bin in each of the distributions includes the overflow. 072009-7 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) opposite-flavor regions, corrected for non-tt̄ backgrounds in total, categorized by the number of b-tagged jets (one or and differences in contributions from leptonic τ-lepton ≥2) as well as the charge and the flavor of the selected decays. This procedure is applied to each bin of the leptons. The signal regions are denoted by 2l-SSp-1b, 2l- distribution under consideration. Figure 1 shows the SSm-1b, 2l-SSp-2b and 2l-SSm-2b, where “p” or “m” BDT distributions for the tt̄ control regions. Agreement indicates the charge of the selected leptons. Considering between the data and the expectation is observed. separate signal regions for positive and negative charges of the leptons increases the sensitivity of the analysis since B. Same-sign dilepton analysis tt̄W events are preferentially produced with positively charged W bosons, while the fake-lepton background The SS dilepton signal regions target the tt̄W process. and other processes such as tt̄Z and tt̄H are expected to Events are required to have two lepton candidates with the be charge symmetric. same sign and pT > 27 GeV. The scalar sum of the pT of The event selection requirements in the SS dilepton selected leptons and jets, HT , is required to be above regions are summarized in Table III. The presence of 240 GeV. Events containing additional loose leptons (with at least four jets and Emiss T > 40 GeV is required in all pT > 7 GeV) are vetoed. Twelve signal regions are defined signal regions except 2μ-SSp-2b and 2μ-SSm-2b. In these 18 ATLAS Data ttW 140 ATLAS Data ttW s = 13 TeV, 36.1 fb-1 Other γ +X s = 13 TeV, 36.1 fb-1 Other γ +X 16 2e-SS-2b-CR (pre-fit) eμ-SS-1b-CR (pre-fit) Charge-flips Fake Leptons 120 Charge-flips Fake Leptons 14 Uncertainty Uncertainty 100 Events / 50 GeV Events / 20 GeV 12 10 80 8 60 6 40 4 20 2 0 0 100 150 200 250 300 350 400 450 500 550 600 0 20 40 60 80 100 120 miss HT [GeV] ET [GeV] (a) (b) ATLAS s = 13 TeV, 36.1 fb-1 Data ttW 3 10 2μ-SS-1b-CR (pre-fit) Other Charge-flips Fake Leptons Uncertainty Events / 20 GeV 102 10 1 20 30 40 50 60 70 80 90 100 110 120 Subleading lepton p [GeV] T (c) FIG. 3. Distributions in fake-lepton control regions: (a) scalar sum of transverse momenta of leptons and jets, HT , in the 2e-SS-2b-CR region, (b) missing transverse momentum, Emiss T , in the eμ-SS-1b-CR region and (c) subleading lepton transverse momentum, pT , in the 2μ-SS-1b-CR region. The shaded band represents the total uncertainty. The “Other” background contains SM processes with small cross sections producing two same-sign prompt leptons. The last bin in each of the distributions includes the overflow. 072009-8 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) ATLAS ATLAS 30 s = 13 TeV, 36.1 fb-1 Data ttW s = 13 TeV, 36.1 fb-1 Data ttW 2μ-SS (pre-fit) Other Fake Leptons 50 2μ-SS (pre-fit) Other Fake Leptons 25 Uncertainty Uncertainty 40 Events / 20 GeV 20 Events 30 15 20 10 5 10 0 0 20 40 60 80 100 120 140 160 180 200 2 3 4 5 6 ≥7 miss ET [GeV] Number of jets (a) (b) 70 ATLAS 140 ATLAS Data ttW Data ttW s = 13 TeV, 36.1 fb-1 Other γ +X s = 13 TeV, 36.1 fb-1 Other γ +X eμ-SS (pre-fit) 120 eμ-SS (pre-fit) 60 Charge-flips Fake Leptons Charge-flips Fake Leptons Uncertainty Uncertainty 50 100 Events / 20 GeV Events 40 80 30 60 20 40 10 20 0 0 40 60 80 100 120 140 160 180 200 4 5 6 ≥7 Emiss T [GeV] Number of jets (c) (d) 30 ATLAS Data ttW ATLAS Data ttW s = 13 TeV, 36.1 fb-1 Other γ +X s = 13 TeV, 36.1 fb-1 Other γ +X 25 2e-SS (pre-fit) 50 2e-SS (pre-fit) Charge-flips Fake Leptons Charge-flips Fake Leptons Uncertainty Uncertainty 20 40 Events / 20 GeV Events 15 30 10 20 5 10 0 0 40 60 80 100 120 140 160 180 200 4 5 6 ≥7 Emiss T [GeV] Number of jets (e) (f) FIG. 4. Distributions in the 2μ-SS, eμ-SS and 2e-SS regions of (a),(c),(e) the missing transverse momentum Emiss T and (b),(d),(f) the jet multiplicity. The shaded band represents the total uncertainty. The “Other” background contains SM processes with small cross sections producing two same-sign prompt leptons. The last bin in each of the distributions includes the overflow. 072009-9 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) TABLE IV. Summary of event selection requirements in the trilepton signal regions targeting the tt̄Z process. Variable 3l-Z-1b4j 3l-Z-2b3j 3l-Z-2b4j 3l-noZ-2b4j Leading lepton pT > 27 GeV Other leptons pT > 20 GeV Sum of lepton charges 1 Z requirement (OSSF pair) jmll − mZ j < 10 GeV jmll − mZ j > 10 GeV njets ≥4 3 ≥4 ≥4 nb-tags 1 ≥2 ≥2 ≥2 TABLE V. Summary of event selection requirements in the trilepton signal regions targeting the tt̄W process. Variable 3lp-noZ-2b2j 3lm-noZ-2b2j 3lp-noZ-1b2j 3lm-noZ-1b2j All leptons pT > 27 GeV Z veto (OSSF pair) jmll − mZ j > 10 GeV njets 2 or 3 HT  >240 GeV Sum of lepton charges þ1 −1 þ1 −1 nb-tags ≥2 ≥2 1 1 regions, the Emiss T requirement is loosened to EmissT > negligible. To enhance the sensitivity of the analysis, the 20 GeV, and at least two jets are required. In the 2e and latter regions are also included in the final fit used to 2μ signal regions, events containing a pair of leptons measure the tt̄W cross section, as discussed in Sec. VII. whose invariant mass is within 10 GeV of the Z boson These six regions are further split according to the charge mass are vetoed. of the leptons, and the resulting twelve regions are The control regions used to measure the fake-lepton denoted by 2l-SS(p,m)-ð1; 2Þb-CR, following the same efficiencies, as explained at the beginning of this section, notation as for the signal regions defined above. In each are defined to be orthogonal to the SS dilepton signal control region, both leptons are required to have regions: either the Emiss T , H T or jet multiplicity require- pT > 27 GeV, and at least one (two) jets are required ments of the signal regions are not satisfied. The tt̄W in the 1b (2b) regions. In addition, events containing a signal contribution in the control regions where both pair of leptons whose invariant mass is compatible with leptons satisfy the tight criteria is found to be non- the Z boson mass are vetoed. The largest contamination 70 80 ATLAS Data ttZ ATLAS Data ttZ s = 13 TeV, 36.1 fb-1 WZ ZZ 70 s = 13 TeV, 36.1 fb-1 WZ ZZ 60 3L-WZ-CR (pre-fit) tZ tWZ 3L-WZ-CR (pre-fit) tZ tWZ Other Fake Leptons Other Fake Leptons Uncertainty 60 Uncertainty 50 Events / 20 GeV Events / 40 GeV 50 40 40 30 30 20 20 10 10 0 0 50 100 150 200 250 0 50 100 150 200 250 300 350 400 Leading lepton p [GeV] Leading jet p [GeV] T T (a) (b) FIG. 5. Distributions of (a) the leading lepton transverse momentum pT and (b) the leading jet pT in the 3l-WZ-CR control region before the fit. The “Other” background contains SM processes with small cross sections producing three prompt leptons. The shaded band represents the total uncertainty. The last bin in each of the distributions includes the overflow. 072009-10 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) from tt̄W is found to be 25%, in the region 2μ- C. Trilepton analysis SSp2b-CR. Eight signal regions with exactly three leptons are The dominant background in the 2l-SS signal regions considered, four of them targeting the tt̄Z and four targeting arises from events containing fake leptons. Backgrounds the tt̄W process, as defined in Tables IV and V, respectively. from the production of prompt leptons with correctly The regions are divided into two groups depending on identified charge come primarily from tt̄H and WZ whether or not a pair of OSSF leptons with invariant production. The charge-flip background is also significant mass within 10 GeV of the Z boson mass is present. in signal regions with two electrons. In regions with two The signal regions are further categorized according muons, this background is negligible as the probability of misidentifying the charge of a muon in the relevant pT to jet and b-tagged jet multiplicities. range is very small. To validate the charge-flip background, The four signal regions in the first group are sensitive to a validation region called 2e-SS-1b-VR is constructed tt̄Z. In the 3l-Z-1b4j region, at least four jets are required, similarly to the 2e-SS signal regions, except that the exactly one of which is b-tagged. In the 3l-Z-2b3j region, number of jets is required to be between one and three, exactly three jets with at least two b-tagged jets are to ensure orthogonality with the signal regions. The required. In the 3l-Z-2b4j region, at least four jets are requirement on HT is also removed, exactly one jet is required, of which at least two are b-tagged. In the 3l-noZ- required to be b-tagged, and the invariant mass of the 2b4j region, targeting events with an off-shell Z or γ , lepton pair is required to be greater than 15 GeV. The at least four jets are required, of which at least two distributions of mll and the leading lepton pT are shown in are b-tagged; no OSSF lepton pair is allowed in the Z Fig. 2, demonstrating good modeling of the charge-flip boson mass window. The sum of the lepton charges must background. be 1. Figure 3 shows the distributions of HT , EmissT and the The remaining four trilepton signal regions target the subleading lepton pT , for the control regions 2e-SS-2b-CR, tt̄W process. These regions require two or three jets and eμ-SS-1b-CR and 2μ-SS-1b-CR. The data and the veto events that contain an OSSF pair of leptons whose expectation agree well, demonstrating the validity of the invariant mass is within 10 GeVof the Z boson mass. In the description of the fake-lepton background determined by first two regions, 3lp-noZ-2b2j and 3lm-noZ-2b2j, at least the matrix method. two jets are required to be b-tagged. In the other two To facilitate comparisons of data with the expectation, regions, 3lp-noZ-1b2j and 3lm-noZ-1b2j, exactly one jet three regions 2e-SS, eμ-SS and 2μ-SS are formed by is required to be b-tagged. The sum of lepton charges is combining all the same-sign signal regions corresponding required to be þ1 (−1) in 3lp-noZ-2b2j and 3lp-noZ-1b2j to a given lepton flavor combination. The distributions of (3lm-noZ-2b2j and 3lm-noZ-1b2j). In regions 3lp-noZ- Emiss T and the number of jets for these three regions are 1b2j and 3lm-noZ-1b2j, HT > 240 GeV is also required. shown in Fig. 4. The signal region definitions for the trilepton channel are 25 ATLAS Data ttW ATLAS 45 Data ttW s = 13 TeV, 36.1 fb-1 Other γ +X s = 13 TeV, 36.1 fb-1 3Lp-noZ2j (pre-fit) 3Lp-noZ2j (pre-fit) Other γ +X 40 Charge-flips Fake Leptons 20 Fake Leptons Uncertainty Uncertainty 35 Events / 25 GeV Events / 20 GeV 30 15 25 20 10 15 10 5 5 0 0 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 120 140 160 180 200 miss Subleading lepton p [GeV] ET [GeV] T (a) (b) FIG. 6. Distributions of (a) the subleading lepton transverse momentum pT and (b) missing transverse momentum Emiss T for events belonging to any of the four trilepton regions targeting the tt̄W process. The distributions are shown before the fit. The “Other” background contains SM processes with small cross sections producing three prompt leptons. The shaded band represents the total uncertainty. The last bin in each of the distributions includes the overflow. 072009-11 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) 50 ATLAS Data ttZ ATLAS Data ttZ ttW WZ 25 s = 13 TeV, 36.1 fb-1 s = 13 TeV, 36.1 fb-1 ttW WZ ZZ tZ 3L-Z-2b4j (pre-fit) tWZ Other 3L-Z-2b4j (pre-fit) tZ tWZ Fake Leptons γ +X Other Fake Leptons 40 Uncertainty 20 γ +X Uncertainty Events / 40 GeV 30 15 Events 20 10 10 5 0 0 4 5 6 7 8 9 0 50 100 150 200 250 300 350 400 Number of jets p (ll) [GeV] T (a) (b) ATLAS Data ttZ s = 13 TeV, 36.1 fb-1 WZ tZ 25 3L-Z-2b4j (pre-fit) tWZ Fake Leptons γ +X Uncertainty 20 Events / 1.33 GeV 15 10 5 0 82 84 86 88 90 92 94 96 98 100 mll [GeV] (c) FIG. 7. Distributions of (a) the number of jets, (b) the transverse momentum pT ðllÞ and (c) the mass mll of the reconstructed Z boson candidate for events in 3l-Z-2b4j. The distributions are shown before the fit. The “Other” background contains SM processes with small cross sections producing three prompt leptons. The shaded band represents the total uncertainty. The last bin in each of the distributions includes the overflow. summarized in Tables IV and V for the signal regions with a Z boson (tZ and tWZ) and Z þ jets production with targeting tt̄Z and tt̄W, respectively. a fake lepton. The dominant backgrounds in the 3l-Z-1b4j, 3l-Z-2b3j A control region is used to determine the normalization and 3l-Z-2b4j signal regions arise from diboson produc- of the WZ þ jets background in data. Exactly three leptons tion, the production of a single top quark in association are required, at least one pair of which must be an OSSF TABLE VI. Definitions of the four signal regions in the tetralepton channel. Region Z2 leptons pT4 pT34 jmZ2 − mZ j Emiss T nb-tags 4l-DF-1b e μ∓  >35 GeV   1 4l-DF-2b e μ∓ >10 GeV    ≥2  ∓  ∓   4l-SF-1b e e ;μ μ  >25 GeV >10 GeV >40 GeV 1 <10 GeV >80 GeV   4l-SF-2b e e∓ ; μ μ∓ >10 GeV  >10 GeV  ≥2 <10 GeV >40 GeV 072009-12 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) pair with an invariant mass within 10 GeV of the Z boson a requirement of EmissT > 40 GeV is applied for events mass. There must be exactly three jets, none of which with jmZ2 − mZ j < 10 GeV. pass the b-tagging requirement. This region is referred to as To suppress events with fake leptons in the 1-b-tag 3l-WZ-CR and it is included in the fit. Distributions multiplicity regions, additional requirements on the scalar comparing data with SM predictions in 3l-WZ-CR are sum of the transverse momenta of the third and fourth shown in Fig. 5, demonstrating good modeling of the WZ leptons (pT34 ) are imposed. In the 4l-SF-1b and 4l-DF-1b background. regions, events are required to satisfy pT34 > 25 GeV and Figure 6 shows the leading lepton pT and Emiss T for events pT34 > 35 GeV, respectively, while in the other regions all belonging to any of the four trilepton regions targeting tt̄W. leptons are required to satisfy pT > 10 GeV. Distributions of the number of jets, the pT and mass of the A control region used to determine the ZZ normaliza- reconstructed Z boson candidate in the signal region most tion, referred to as 4l-ZZ-CR, is included in the fit and is sensitive to tt̄Z, 3l-Z-2b4j, are shown in Fig. 7. defined to have exactly four reconstructed leptons, a Z2 pair with OSSF leptons, the value of both mZ1 and mZ2 within D. Tetralepton analysis 10 GeV of the mass of the Z boson, and 20 GeV < Emiss T < 40 GeV. The leading lepton pT and the jet multiplicity in The tetralepton channel targets the tt̄Z process for the this control region are shown in Fig. 8, and good agreement case where both W bosons, resulting from top-quark is seen between data and prediction. decays, and the Z boson decay leptonically. Events with The contribution from backgrounds containing fake two pairs of opposite-sign leptons are selected, and at least leptons is estimated from simulation and corrected with one pair must have the same flavor. The OSSF lepton pair scale factors determined in two control regions: one region with reconstructed invariant mass closest to mZ is attributed enriched in tt̄ events and one region enriched in Z þ jets to the Z boson decay and denoted in the following by Z1. events. The scale factors are extracted and applied sepa- The two remaining leptons are used to define Z2 . The signal rately for electron and muon fake-lepton candidates, and region definitions for the tetralepton channel are summa- for leptons arising from heavy-flavor hadrons and other rized in Table VI. Four signal regions are defined according sources. Therefore, a total of four scale factors are to the relative flavor of the two Z2 leptons, different flavor determined. The scale factors are applied to all MC (DF) or same flavor (SF), and the number of b-tagged jets: simulation events with fewer than four prompt leptons one, or at least two (1b, 2b). The signal regions are thus according to the number, flavor and origin of the fake 4l-DF-1b, 4l-DF-2b, 4l-SF-1b and 4l-SF-2b. leptons. It is verified that the scale factors for different In the same-flavor regions, requirements on Emiss T are generators used in the simulation are consistent with applied to suppress the ZZ background. In the 4l-SF-1b each other. signal region, the EmissT is required to be greater than Figure 9 compares the data with the expected distribu- 80 GeV (40 GeV) for events with jmZ2 − mZ j < 10 GeV tions for all four signal regions combined, showing good (jmZ2 − mZ j > 10 GeV). In the 4l-SF-2b signal region, agreement between data and expectation. 120 ATLAS ATLAS 100 Data ZZ Data ZZ s = 13 TeV, 36.1 fb-1 s = 13 TeV, 36.1 fb-1 4L-ZZ-CR (pre-fit) Fake Leptons Other 100 4L-ZZ-CR (pre-fit) Fake Leptons Other 80 Uncertainty Uncertainty 80 Events / 30 GeV 60 Events 60 40 40 20 20 0 0 40 60 80 100 120 140 160 180 200 220 0 1 ≥2 Leading lepton p [GeV] Number of jets T (a) (b) FIG. 8. Distribution of (a) the leading lepton transverse momentum pT and (b) jet multiplicity in the 4l-ZZ-CR control region. The distributions are shown before the fit. The shaded band represents the total uncertainty. The last bin in each of the distributions includes the overflow. 072009-13 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) 35 50 ATLAS Data ttZ ATLAS Data ttZ s = 13 TeV, 36.1 fb-1 Other ZZ s = 13 TeV, 36.1 fb-1 Other ZZ 30 4L-comb (pre-fit) 4L-comb (pre-fit) tWZ Fake Leptons tWZ Fake Leptons 40 Uncertainty Uncertainty 25 Events / 8 GeV 20 30 Events 15 20 10 10 5 0 0 1 2 3 4 ≥5 70 75 80 85 90 95 100 105 110 Number of jets mZ1 [GeV] (a) (b) 30 ATLAS 25 ATLAS Data ttZ Data ttZ s = 13 TeV, 36.1 fb-1 Other ZZ s = 13 TeV, 36.1 fb-1 Other ZZ 25 4L-comb (pre-fit) 4L-comb (pre-fit) tWZ Fake Leptons tWZ Fake Leptons Uncertainty 20 Uncertainty 20 Events / 0.5 rad Events / 0.5 15 15 10 10 5 5 0 0 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 3 Δη (leptons from Z ) Δφ (leptons from Z ) 1 2 (c) (d) FIG. 9. Distributions, for all tetralepton signal regions combined, of (a) the number of jets, (b) the invariant mass of the OSSF lepton pair closest to the Z boson mass, mZ1 , (c) the pseudorapidity separation Δη for that pair of leptons and (d) the azimuthal angle Δϕ between the remaining two leptons. The “Other” background contains SM processes with small cross sections producing four prompt leptons. The distributions are shown before the fit. The shaded band represents the total uncertainty. The first and last bin include the underflow and overflow, respectively. VI. SYSTEMATIC UNCERTAINTIES from a calibration of the luminosity scale using x-y beam- separation scans. This systematic uncertainty affects all The signal and background yields in each signal and processes modeled using Monte Carlo simulations, apart control region may be affected by several sources of from Z þ 1HF, Z þ 2HF, WZ and ZZ, whose normaliza- systematic uncertainty. These are implemented as nuisance tions are taken from data control regions. parameters in the fit, explained in Sec. VII, are constrained by Gaussian probability density functions and are described in the following subsections. B. Uncertainties associated with reconstructed objects Uncertainties associated with the lepton selection arise A. Luminosity from the trigger, reconstruction, identification and isolation The uncertainty in the integrated luminosity of the efficiencies, and lepton momentum scale and resolution dataset is 2.1%. It is derived, following a methodology [59,71–73]. similar to that detailed in Ref. [23], and using the LUCID-2 Uncertainties associated with the jet selection arise from detector for the baseline luminosity measurements [24], the jet energy scale (JES), the JVT requirement and the jet 072009-14 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) energy resolution (JER). The JES and its uncertainty are D. Uncertainties in the background modeling derived by combining information from test-beam data, The Z þ jets process is, together with tt̄ production, the collision data and simulation [64]. The uncertainties in the dominant background in the OS dilepton channel. Its JER and JVT have a significant effect at low jet pT . normalization is extracted from data as described in The efficiency of the flavor-tagging algorithm is mea- Sec. VA, but the shape of the BDT distribution is obtained sured for each jet flavor using control samples in data and from simulation. To assess the systematic uncertainty in the in simulation. From these measurements, correction factors shape, the renormalization, factorization and resummation are derived to correct the tagging rates in the simulation. In scales used in the MC generation are varied by a factor of the case of b-jets, correction factors and their uncertainties two with respect to the nominal values. are estimated from data using dileptonic tt̄ events [66]. In The normalization and shape of the tt̄ background in the case of c-jets, they are derived using jets from W boson the OS dilepton channel is obtained using the data-driven decays in tt̄ events [74]. In the case of light-flavor jets, method detailed in Sec. VA. A systematic uncertainty correction factors are derived using dijet events [75]. arises from the factor used to obtain tt̄ background yields Sources of uncertainty affecting the b- and c-tagging in the same-flavor signal regions from corresponding efficiencies are considered as a function of jet pT , including opposite-flavor dilepton control regions. The uncertainty bin-to-bin correlations [76]. The uncertainty in the effi- is due to the finite size of the samples of simulated ciency for tagging light-flavor jets depends on the jet pT events used, and the difference between the values of the and on η. These systematic uncertainties are taken as factor obtained with the nominal POWHEG-BOX+PYTHIA 8 uncorrelated between b-jets, c-jets, and light-flavor jets. sample and an alternative sample generated using An additional uncertainty is assigned to account for the MG5_aMC+PYTHIA 8. The total uncertainty in the factor extrapolation of the b-tagging efficiency measurement from is found to be 3%. the pT region used to determine the correction factors to In the trilepton regions sensitive to tt̄Z, the normalization regions with higher transverse momentum. of the WZ background is treated as a free parameter in the The treatment of the uncertainties associated with fit used to extract the tt̄Z and tt̄W signals. The uncertainty reconstructed objects is common to all analysis channels, in the extrapolation of the WZ background estimate from and thus these are considered as fully correlated among the control region to signal regions with specific jet and different analysis regions. b-tag multiplicities is evaluated by comparing predictions obtained by varying the renormalization, factorization C. Uncertainties in the signal modeling and resummation scales used in MC generation. The Four sources of systematic uncertainties in the theoreti- uncertainties vary from 30% to 50%, depending on the cal predictions of the tt̄Z and tt̄W processes are considered. signal region. These signal modeling uncertainties are treated as uncorre- The normalization of the ZZ background is treated as a lated between the two processes, and correlated among free parameter in the fit. An additional uncertainty arises channels. Taking instead the uncertainties as correlated from the extrapolation from the 4l-ZZ-CR control region between the two processes has a negligible impact on the to the signal regions. It is assessed by varying the results. Acceptance effects due to the choice of scale and renormalization, factorization and resummation scales used PDF in the nominal MG5_aMC+PYTHIA 8 (A14 tune) in MC generation, and found to be in the range 20%–40%. sample are considered. The renormalization and factoriza- The uncertainty in the tt̄H background is evaluated by tion scales μR ¼ μF are varied simultaneously by factors 2.0 varying the factorization and renormalization scales up and and 0.5. In addition, the effects of a set of variations in the down by a factor of two with respect to the nominal values. tune parameters (A14 eigentune variations), sensitive to It is found to be around 10%. initial- and final-state radiation, multiple parton interactions An overall normalization uncertainty of 30% is assigned and color reconnection, are evaluated [36]. Studies per- to the tZ background, motivated by the measurements formed at particle level show that the largest impact comes of this process presented in Refs. [78,79]. An additional from variations in initial-state radiation [77]. The system- uncertainty affecting the distribution of this background as atic uncertainty due to the choice of generator for the tt̄Z a function of jet and b-tagged jet multiplicities is evaluated and tt̄W acceptance is estimated by comparing the nominal by varying the factorization and renormalization scales, as sample with one generated with SHERPA v2.2. The SHERPA well as the amount of radiation in the Perugia2012 sample uses the LO matrix element with up to one (two) parton-shower tune. additional parton(s) included in the matrix element calcu- An uncertainty of 10% is assigned to the tWZ back- lation for tt̄Z (tt̄W) and merged with the SHERPA parton ground cross section, resulting from different prescriptions shower [43] using the ME+PS@LO prescription. The for removing the interference with the tt̄Z process. The NNPDF3.0NLO PDF set is used in conjunction with a shape uncertainty is evaluated by varying the factorization dedicated parton-shower tune developed by the SHERPA and renormalization scales up and down by a factor of two authors. with respect to the nominal value. 072009-15 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) For other prompt-lepton backgrounds, uncertainties of measurement of the fake-lepton efficiencies. For fake-lepton 20% are assigned to the normalizations of the WH and efficiencies in events with one (at least two) b-tagged jet(s), ZH processes, based on calculations from Ref. [34]. An seven (four) bins are used, and there is one nuisance parameter uncertainty of 50% is considered for triboson and same- for each of the two lepton flavors. In the trilepton signal sign WW processes. regions targeting tt̄Z, where the fake-lepton background is A 10% uncertainty is applied to the charge-flip back- less important, a simplified description of the fake-lepton ground, resulting from uncertainties in the charge-flip rates uncertainties is used, with one nuisance parameter for each of extracted from a control sample as described in Sec. V. the two lepton flavors. These nuisance parameters correspond A 30% uncertainty is assigned to the contribution from to the maximum of the up and down shifts of the fake-lepton events with two prompt leptons or one prompt lepton and a efficiencies resulting from statistical uncertainties and the photon conversion in the control regions used to measure prompt lepton background subtraction in the control regions the fake-lepton efficiency. In the SS dilepton channel used to measure the fake-lepton efficiency. The uncertainties regions and trilepton regions targeting tt̄W, there are 22 in the fake-lepton background in the tt̄Z and tt̄W analysis nuisance parameters corresponding to the statistical uncer- regions are considered to be uncorrelated, due to the tainty in the measurement of the fake-lepton efficiencies. different lepton selection requirements used in the two sets One nuisance parameter is used for each pT bin used in the of regions. 500 450 ATLAS Data ttZ ATLAS Data ttZ s = 13 TeV, 36.1 fb-1 tt Z + 2 HF s = 13 TeV, 36.1 fb-1 tt Z + 2 HF 400 2L-Z-6j1b (post-fit) 2L-Z-5j2b (post-fit) Z + 1 HF Z + 0 HF Z + 1 HF Z + 0 HF 400 Other Uncertainty 350 Other Uncertainty 300 Events / 0.1 Events / 0.1 300 250 200 200 150 100 100 50 0 0 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 BDT output BDT output (a) (b) 200 ATLAS Data ttZ s = 13 TeV, 36.1 fb-1 tt Z + 2 HF 180 2L-Z-6j2b (post-fit) Z + 1 HF Z + 0 HF 160 Other Uncertainty 140 Events / 0.1 120 100 80 60 40 20 0 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 BDT output (c) FIG. 10. The BDT distributions for the OS dilepton signal regions, (a) 2l-Z-6j1b, (b) 2l-Z-5j2b, (c) 2l-Z-6j2b. The distributions are shown after the fit. The “Other” background contains SM processes with small cross sections producing two opposite-sign prompt leptons. The shaded band represents the total uncertainty. The last bin of each distribution contains the overflow. 072009-16 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) Uncertainties in scale factors applied to the fake-lepton channel, the four signal regions 4l-DF-1b, 4l-DF-2b, 4l- background are taken into account in the fake-lepton SF-1b and 4l-SF-2b and the control region 4l-ZZ-CR are background yield in the tetralepton channel and the tt̄γ included in the fit. background contribution in the trilepton and 2l-SS chan- The fit is based on the profile-likelihood technique, nels. These uncertainties are associated with reconstructed where systematic uncertainties are included in the fit as objects and the limited sizes of control regions in which nuisance parameters constrained by Gaussian functions. the scale factors are obtained. The scale factors have None of the uncertainty parameters are found to be uncertainties between 10% and 50%, depending on the significantly constrained or pulled in the fit. The calculation fake-lepton flavor and source. The 2l-SS and trilepton of confidence intervals and hypothesis testing is performed fake-lepton systematic uncertainties from the matrix using a modified frequentist method as implemented in method are assumed to be uncorrelated with the systematic RooStats [80,81]. uncertainties in the fake-lepton scale factors. Figure 10 shows the BDT output distribution in signal regions 2l-Z-6j1b, 2l-Z-5j2b and 2l-Z-6j2b after perform- VII. RESULTS ing the fit. Figures 11 and 12 summarize the comparison between data and the post-fit signal and background yields The signal strengths μtt̄Z and μtt̄W , defined as the ratios of for regions sensitive to tt̄Z and tt̄W production, together the measured values of the inclusive production cross with the relevant control regions. In all cases, good sections to the corresponding SM predictions discussed agreement between observed values and the expectation in Sec. III, are extracted simultaneously using a binned is seen. The normalization corrections for the WZ and ZZ maximum-likelihood fit to the numbers of events in the backgrounds with respect to the predictions are obtained dilepton, trilepton and tetralepton signal and control from the fits as described in Sec. V and found to be regions. In the OS dilepton channel signal regions 2l-Z- compatible with unity: 0.91  0.10 for the WZ background 6j1b, 2l-Z-5j2b and 2l-Z-6j2b, the BDT output distribu- and 1.11  0.17 for the ZZ background. The normaliza- tion is fitted. In the SS dilepton channel, the twelve signal tions of the Z þ 1HF and Z þ 2HF backgrounds are regions 2l-SSp-1b, 2l-SSm-1b, 2l-SSp-2b and 2l-SSm- mainly constrained in the low BDT output bins of the 2b are fitted together with the twelve control regions OS dilepton channel signal regions, where the signal 2l-SSp-1b-CR, 2l-SSm-1b-CR, 2l-SSp-2b-CR and contamination is low. Their values are found to be 1.19  2l-SSm-2b-CR defined in Sec. V. The contribution from 0.25 and 1.09  0.13, respectively. the tt̄W signal in the SS dilepton control regions is taken In addition to the combined fit described above, fits in into account in the fit. The dependence of the fake-lepton individual channels are performed. The tt̄Z signal strength background in these regions on the tt̄W signal strength is is extracted through fits to the opposite-sign dilepton also taken into account. In the trilepton channel, the eight regions alone, to the trilepton channel regions alone and signal regions described in Sec. V are included in the fit, as to the tetralepton channel signal regions alone. The tt̄W is the 3l-WZ-CR control region. Finally, in the tetralepton signal strength is extracted using the four trilepton signal 103 ATLAS Data ttZ ATLAS Data ttZ 103 ttW WZ s = 13 TeV, 36.1 fb-1 s = 13 TeV, 36.1 fb-1 ZZ tWZ ZZ tZ (post-fit) tWZ Other (post-fit) Other Fake Leptons Fake Leptons γ +X Uncertainty Uncertainty 102 2 10 Events Events 10 10 1 Data / Pred. Data / Pred. 1.5 1.5 1 1 0.5 3L-Z 3L-Z 3L-Z 3L-n 3L-W 0.5 4L-S 4L-S 4L-D 4L-D 4L-Z -1b4 -2b4 -2b3 oZ- Z-C F-1 F-2 F-1 F-2 Z-C j j j 2b4 R b b b b R j (a) (b) FIG. 11. Event yields in data compared with the results of the fit that extracts σ tt̄Z and σ tt̄W simultaneously in the (a) trilepton and (b) tetralepton signal regions targeting the tt̄Z process. Yields for the control regions used to extract the normalization of the WZ and ZZ backgrounds are also shown. The “Other” background summarizes all small SM backgrounds described in Sec. III. The shaded band represents the total uncertainty. 072009-17 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) 103 ATLAS Data ttW s = 13 TeV, 36.1 fb-1 ttZ WZ (post-fit) Other ttH Charge-flips γ +X Fake Leptons Uncertainty 102 Events 10 1 Data / Pred. 1.5 1 0.5 3Lm-noZ-2b2j 3Lm-noZ-1b2j ee-SSm-2b-SR 3Lp-noZ-2b2j ee-SSm-1b-SR 3Lp-noZ-1b2j eμ-SSp-1b-CR μμ-SSp-1b-CR eμ-SSp-2b-CR μμ-SSp-2b-CR ee-SSm-1b-CR ee-SSm-2b-CR ee-SSp-2b-SR ee-SSp-1b-SR μμ-SSm-2b-SR eμ-SSm-2b-SR μμ-SSm-1b-SR eμ-SSm-1b-SR ee-SSp-1b-CR ee-SSp-2b-CR eμ-SSm-1b-CR μμ-SSm-1b-CR eμ-SSm-2b-CR μμ-SSm-2b-CR μμ-SSp-2b-SR eμ-SSp-2b-SR μμ-SSp-1b-SR eμ-SSp-1b-SR FIG. 12. Event yields in data compared with the results of the fit that extracts σ tt̄Z and σ tt̄W simultaneously in the regions targeting the tt̄W process. The “Other” background summarizes all small SM backgrounds described in Sec. III. The shaded band represents the total uncertainty. regions targeting tt̄W and the same-sign dilepton regions For the tt̄Z process, both the observed and the expected considered in the combined fit. The measured values of the significances are found to be much larger than five standard signal strengths μtt̄Z and μtt̄W are reported in Table VII for deviations. For the tt̄W process, an excess of events over each channel separately and for the combined fit. the expected background-only hypothesis is found with an Agreement is observed for the measured values between all the different fit configurations. The measured signal strengths from the combined fit and 1.6 ATLAS Best fit -1 their uncertainties are converted to inclusive cross-section s = 13 TeV, 36.1 fb 68% CL measurements using the signal simulation described in 95% CL 1.4 Sec. III and the central values of the theoretical predictions. ttZ cross section [pb] The results are: σ tt̄Z ¼ 0.95  0.08stat  0.10syst pb ¼ NLO prediction 0.95  0.13 pb and σ tt̄W ¼ 0.87  0.13stat  0.14syst pb ¼ 1.2 0.87  0.19 pb. Figure 13 shows a comparison of the fit þ0.09 results with theoretical predictions, σ th tt̄Z ¼ 0.88−0.11 pb þ0.08 1 and σ th tt̄W ¼ 0.60−0.07 pb, demonstrating good agreement between the measured and predicted cross sections. 0.8 TABLE VII. Measured signal strengths of tt̄Z and tt̄W for different fit configurations and the combined fit. The uncertain- 0.6 ties include statistical and systematic components. 0.4 0.6 0.8 1 1.2 1.4 1.6 Fit configuration μtt̄Z μtt̄W ttW cross section [pb] Combined 1.08  0.14 1.44  0.32 FIG. 13. The result of the simultaneous fit to the tt̄Z and tt̄W 2l-OS 0.73  0.28  cross sections along with the 68% and 95% confidence level 3ltt̄Z 1.08  0.18  (C.L.) contours. The cross shows the SM calculations and their 2l-SS and 3ltt̄W  1.41  0.33 uncertainties, including renormalization and factorization scale 4l 1.21  0.29  uncertainties as well as uncertainties including αS variations. 072009-18 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) TABLE VIII. List of relative uncertainties in the measured TABLE IX. Effective field theory operators considered and cross sections of the tt̄Z and tt̄W processes from the fit, grouped their form in terms of SM fields. The notation of Ref. [85] is used. in categories. All uncertainties are symmetrized. The sum in quadrature may not be equal to the total due to correlations Operator Expression between uncertainties introduced by the fit. ð3Þ ↔I OϕQ ðϕ† iDμ ϕÞðQ̄γ μ τI QÞ ↔ Uncertainty σ tt̄Z σ tt̄W ð1Þ OϕQ ðϕ† iDμ ϕÞðQ̄γ μ QÞ Luminosity 2.9% 4.5% Oϕt ↔ ðϕ† iDμ ϕÞðt̄γ μ tÞ Simulated sample statistics 2.0% 5.3% OtW ðQ̄σ μν τI tÞϕ̃W Iμν Data-driven background statistics 2.5% 6.3% JES=JER 1.9% 4.1% OtB ðQ̄σ μν tÞϕ̃Bμν Flavor tagging 4.2% 3.7% Other object-related 3.7% 2.5% Data-driven background normalization 3.2% 3.9% Modeling of backgrounds from simulation 5.3% 2.6% The operators are defined in Table IX, following Ref. [85]. Background cross sections 2.3% 4.9% The first two operators enter the ttZ vertex as a linear Fake leptons and charge misID 1.8% 5.7% combination, such that the measurement is sensitive to the ð3Þ ð1Þ tt̄Z modeling 4.9% 0.7% difference CϕQ − CϕQ . For this paper, the effect of this tt̄W modeling 0.3% 8.5% ð3Þ ð1Þ combination is evaluated by varying CϕQ with CϕQ set Total systematic 10% 16% Statistical 8.4% 15% to zero. Considering only one EFT operator at a time, any Total 13% 22% observable, such as the tt̄Z event rate in a certain signal region, can be expressed as a quadratic function of the coefficient Ci : observed (expected) significance of 4.3 (3.4) standard deviations. The significance values are computed using Ci ð1Þ C2i ð2Þ σ tot;i ¼ σ SM þ σ þ 2 i σ : ð1Þ the asymptotic approximation described in Ref. [82]. ðΛ=1 TeVÞ ðΛ=1 TeVÞ4 ii Table VIII shows the uncertainties in the measured tt̄Z and tt̄W cross sections, grouped in categories, along with The term linear in Ci on the right-hand side of Eq. (1) the total uncertainties. For both processes, the precision of results from the interference of the BSM operators with the the measurement is affected by statistical and systematic SM. For Ci =Λ2 of order 1 TeV−2, the interference term uncertainties in similar proportions. For the tt̄Z determi- ð3Þ dominates in Eq. (1) for OϕQ and Oϕt , while the quadratic nation, the dominant systematic uncertainty sources are the term dominates for OtW and OtB . modeling of the backgrounds and of the signal. For the tt̄W ð1Þ ð2Þ determination, the dominant systematic uncertainty sources The values of σ i and σ ii are computed using simulated are the modeling of the signal and the limited amount of event samples generated with MG5_aMC interfaced to data available in the control regions and simulated event PYTHIA 8 [11,86,87]. The computation is performed at samples. NLO, separately for all trilepton and tetralepton signal regions. The detector reconstruction efficiency is verified to be compatible between SM tt̄Z samples and samples with VIII. INTERPRETATION nonzero values of Ci , for ranges of Ci considered here. The effective field theory (EFT) framework provides a A fit is then performed to extract Ci =Λ2 . The fit is model-independent approach to the parametrization of similar to the one described in Sec. VII, except that only possible deviations from the SM predictions. In this the four trilepton and four tetralepton signal regions framework, effects due to BSM physics are described by targeting tt̄Z are used and a normalization uncertainty of adding additional operators of dimension six or higher to 12%, corresponding to the uncertainty in the NLO cross- the SM Lagrangian. Each EFT operator Oi is associated section computation, is applied to the SM tt̄Z prediction. with a Wilson coefficient Ci , and the operators enter the Uncertainties resulting from the limited sizes of MC ð1Þ ð2Þ modified Lagrangian in the form ðCi =Λ2 ÞOi , where Λ is samples used to derive the values of σ i and σ ii are the characteristic energy scale of the BSM physics. propagated to the measured values of Ci =Λ2 . The complete set of independent, gauge-invariant and The profile-likelihood test statistic is defined as baryon-number conserving EFT operators at dimension six −Δ logðLÞ ¼ logðLðĈi Þ=LðCi ÞÞ, where L is the profile contains 59 different operators [83,84]. In the present likelihood as a function of the Wilson coefficient Ci , analysis, five of these operators are considered, all of and Ĉi is the best-fit value of Ci . Approximate confidence ð3Þ ð1Þ which modify the ttZ vertex: OϕQ , OϕQ , Oϕt , OtW , OtB . intervals for the Wilson coefficients are computed using the 072009-19 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) TABLE X. The expected and observed 68% and 95% confidence intervals, which include the value 0, for Ci =Λ2 ð3Þ ð3Þ ð1Þ for the EFT coefficients CϕQ , Cϕt , CtB and CtW . The intervals for CϕQ are derived setting CϕQ to zero; the ð3Þ ð1Þ measurement is sensitive to the difference CϕQ − CϕQ . All results are obtained by varying one coefficient at the time and are given in units of 1=TeV2 . Previous indirect 68% C.L. constraints [88] are also quoted. The previous direct ð3Þ constraints at 95% C.L. are obtained from Ref. [10] for Cϕt and CtB and from Refs. [89,90] for CϕQ and CtW , using Ref. [83] to translate the measurements into limits on the coefficients. Limits from fits for the EFT coefficients with only the linear term are also shown. Coefficients ð3Þ CϕQ =Λ2 Cϕt =Λ2 CtB =Λ2 CtW =Λ2 Previous indirect constraints at 68% C.L. ½−4.7; 0.7 ½−0.1; 3.7 ½−0.5; 10 ½−1.6; 0.8 Previous direct constraints at 95% C.L. ½−1.3; 1.3 ½−9.7; 8.3 ½−6.9; 4.6 ½−0.2; 0.7 Expected limit at 68% C.L. ½−2.1; 1.9 ½−3.8; 2.7 ½−2.9; 3.0 ½−1.8; 1.9 Expected limit at 95% C.L. ½−4.5; 3.6 ½−23; 4.9 ½−4.2; 4.3 ½−2.6; 2.6 Observed limit at 68% C.L. ½−1.0; 2.7 ½−2.0; 3.5 ½−3.7; 3.5 ½−2.2; 2.1 Observed limit at 95% C.L. ½−3.3; 4.2 ½−25; 5.5 ½−5.0; 5.0 ½−2.9; 2.9 Expected limit at 68% C.L. (linear) ½−1.9; 2.0 ½−3.0; 3.2   Expected limit at 95% C.L. (linear) ½−3.7; 4.0 ½−5.8; 6.3   Observed limit at 68% C.L. (linear) ½−1.0; 2.9 ½−1.8; 4.4   Observed limit at 95% C.L. (linear) ½−2.9; 4.9 ½−4.8; 7.5   formula −Δ logðLÞ ¼ ε, where the threshold ε is set to 0.5 four leptons are analyzed. The tt̄Z and tt̄W production and 1.92 for the 68% (1σ) and 95% confidence levels cross sections are determined to be σ tt̄Z ¼ 0.95  0.08stat  (C.L.), respectively. 0.10syst pb ¼ 0.95  0.13 pb and σ tt̄W ¼ 0.87  0.13stat  The confidence intervals for Ci are computed consider- 0.14syst pb ¼ 0.87  0.19 pb. The measured values are ing only the minimum of λðCi Þ near Ci ¼ 0. For coefficient consistent with the SM predictions. The measurements ð3Þ CϕQ (Cϕt ), another, deeper minimum exists for negative are used to derive confidence intervals for the Wilson values of Ci ∼ 30ð20Þ, which is excluded by previous coefficients of dimension-6 effective field theory operators constraints. The 68% and 95% confidence intervals are involving the top quark and the Z boson. shown in Table X, together with previous constraints on the EFT coefficients obtained from Refs. [10,88–90]. The ACKNOWLEDGMENTS lower boundary of the 95% confidence interval for Cϕt is We thank CERN for the very successful operation of the at large negative values, which are excluded by indirect LHC, as well as the support staff from our institutions constraints. The tt̄Z measurement provides competitive without whom ATLAS could not be operated efficiently. constraints for positive Cϕt values. The full likelihood scans We acknowledge the support of ANPCyT, Argentina; are shown in Fig. 14 in the Appendix. YerPhI, Armenia; ARC, Australia; BMWFW and FWF, The fits are repeated while assuming that the quadratic Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and terms are zero, and the results of these fits are also reported FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; in Table X. For CtW and CtB , where the quadratic terms CONICYT, Chile; CAS, MOST and NSFC, China; dominate, the fits do not converge. Compared with the COLCIENCIAS, Colombia; MSMT CR, MPO CR and ð3Þ nominal fits for CϕQ and Cϕt , the limits shift to larger values, VSC CR, Czech Republic; DNRF and DNSRC, Denmark; consistent with removing a positive term from the pre- IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, diction. The most notable change is the improvement in the Georgia; BMBF, HGF, and MPG, Germany; GSRT, lower limit for Cϕt at 95% C.L., as the second minimum Greece; RGC, Hong Kong SAR, China; ISF and disappears when a linear expression is assumed. Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; IX. CONCLUSION MNE/IFA, Romania; MES of Russia and NRC KI, Measurements of the production cross sections of a top- Russian Federation; JINR; MESTD, Serbia; MSSR, quark pair in association with a Z or W boson using Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South pffiffiffi 36.1 fb−1 of data collected by the ATLAS detector in s ¼ Africa; MINECO, Spain; SRC and Wallenberg Foundation, 13 TeV pp collisions at the LHC are presented. Final states Sweden; SERI, SNSF and Cantons of Bern and Geneva, with two same- or opposite-sign leptons, three leptons or Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, 072009-20 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) United Kingdom; DOE and NSF, United States of America. Society and Leverhulme Trust, United Kingdom. The In addition, individual groups and members have received crucial computing support from all WLCG partners is support from BCKDF, CANARIE, CRC and Compute acknowledged gratefully, in particular from CERN, the Canada, Canada; COST, ERC, ERDF, Horizon 2020, and ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF Marie Skłodowska-Curie Actions, European Union; (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/ Investissements d’ Avenir Labex and Idex, ANR, France; GridKA (Germany), INFN-CNAF (Italy), NL-T1 DFG and AvH Foundation, Germany; Herakleitos, Thales (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and Aristeia programmes co-financed by EU-ESF and the and BNL (USA), the Tier-2 facilities worldwide and large Greek NSRF, Greece; BSF-NSF and GIF, Israel; CERCA non-WLCG resource providers. Major contributors of Programme Generalitat de Catalunya, Spain; The Royal computing resources are listed in Ref. [91]. APPENDIX: ADDITIONAL MATERIAL The Appendix shows the profile-likelihood test statistic for the four EFT coefficients and the input variables used for the OS dilepton BDT. 5 5 3σ 3σ 4 4 Observed 3 3 Expected -Δ log(L) -Δ log(L) 2σ 2σ 2 2 Observed Expected 1 1 1σ 1σ 0 0 ATLAS ATLAS s = 13 TeV 36.1 fb-1 s = 13 TeV 36.1 fb-1 −1 −1 40 −30 −20 −10 0 10 −30 −25 −20 −15 −10 −5 0 5 10 (3) CφQ/ Λ2 Cφt/ Λ2 (a) (b) 5 5 3σ 3σ 4 4 Observed Observed 3 Expected 3 Expected -Δ log(L) -Δ log(L) 2σ 2σ 2 2 1 1 1σ 1σ 0 0 ATLAS ATLAS -1 s = 13 TeV 36.1 fb s = 13 TeV 36.1 fb-1 −1 −1 −8 −6 −4 −2 0 2 4 6 8 −5 −4 −3 −2 −1 0 1 2 3 4 5 CtB/ Λ2 CtW/ Λ2 (c) (d) ð3Þ ð3Þ FIG. 14. The value of the profile-likelihood test statistic as a function of c=Λ2 , for (a) CϕQ , (b) Cϕt , (c) CtB , and (d) CtW . In the CϕQ and Cϕt distributions, another, deeper minimum exists for large negative values of Ci , which is excluded by indirect measurements. There, the vertical axis is chosen such that the value of the likelihood at the minimum near Ci ¼ 0 is zero. 072009-21 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) TABLE XI. The definitions and ranking of input variables for the BDT in the OS dilepton analysis. Jets and leptons are ordered in descending order of pT . Only the first eight jets are considered when calculating the input variables. Ranking Definition 6j1b 5j2b 6j2b pT of the lepton pair 8 11 8 pT of the fourth jet 6 12 6 pT of the fifth jet  14  pT of the sixth jet 9  11 ΔRη between the two leptons 7 8 12 Number of jet pairs with mass within a window of 30 GeV around 85 GeV 4 6 4 Number of three-jet combinations (containing exactly one b-tagged jet) compatible with a top quark   17 (jmbjj − mt j < 15 GeV) and (jmjj − mW j < 15 GeV) Invariant mass of the two jets with the smallest ΔRη 13 7 14 Invariant mass of the two untagged jets with the highest pT 15 13  Invariant mass of the two jets with the highest value of the b-tagging discriminant  10 9 Scalar sum of pT divided by the sum of energy of all jets 2 1 2 Average ΔRη of all jet pairs 5 4 5 Maximum invariant mass of a lepton and the b-tagged jet with the smallest ΔRη 14  13 First Fox–Wolfram moment built from jets and leptons 3 2 1 Sum of jet pT , using up to six jets 12 5 10 η of dilepton system 1 3 3 Sum of the two closest two-jet invariant masses from jjj1 and jjj2 divided by two 10  15 ΔRη between two jets with the highest value of the b-tagging discriminant in the event  9 7 pT of the b-tagged jet with the highest pT 11  16 [1] ATLAS Collaboration, Evidence for the associated [8] ATLAS Collaboration, Measurements of inclusive and production of the Higgs boson and a top quark pair differential fiducial cross-sections of tt̄γ production in pffiffiffi with the ATLAS detector, Phys. 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Casha,164 D. W. Casper,168 R. Castelijn,118 F. L. Castillo,171 V. Castillo Gimenez,171 N. F. Castro,137a,137e A. Catinaccio,35 J. R. Catmore,131 A. Cattai,35 J. Caudron,24 V. Cavaliere,29 E. Cavallaro,14 D. Cavalli,66a M. Cavalli-Sforza,14 V. Cavasinni,69a,69b E. Celebi,12b F. Ceradini,72a,72b L. Cerda Alberich,171 A. S. Cerqueira,78a A. Cerri,153 L. Cerrito,71a,71b F. Cerutti,18 A. Cervelli,23b,23a S. A. Cetin,12b A. Chafaq,34a D. Chakraborty,119 S. K. Chan,57 W. S. Chan,118 W. Y. Chan,88 J. D. Chapman,31 B. Chargeishvili,156b D. G. Charlton,21 C. C. Chau,33 C. A. Chavez Barajas,153 S. Che,123 A. Chegwidden,104 S. Chekanov,6 S. V. Chekulaev,165a G. A. Chelkov,77,k M. A. Chelstowska,35 B. Chen,76 C. Chen,58a C. H. Chen,76 H. Chen,29 J. Chen,58a J. Chen,38 S. Chen,134 S. J. Chen,15c X. Chen,15b,l Y. Chen,80 Y-H. Chen,44 H. C. Cheng,61a H. J. Cheng,15d A. Cheplakov,77 E. Cheremushkina,121 R. Cherkaoui El Moursli,34e E. Cheu,7 K. Cheung,62 T. J. A. Chevalérias,142 L. Chevalier,142 V. Chiarella,49 G. Chiarelli,69a G. Chiodini,65a A. S. Chisholm,35,21 A. Chitan,27b I. Chiu,160 Y. H. Chiu,173 M. V. Chizhov,77 K. Choi,63 A. R. Chomont,129 S. Chouridou,159 Y. S. Chow,118 V. Christodoulou,92 M. C. Chu,61a J. Chudoba,138 A. J. Chuinard,101 J. J. Chwastowski,82 L. Chytka,127 D. Cinca,45 V. Cindro,89 I. A. Cioară,24 A. Ciocio,18 F. Cirotto,67a,67b Z. H. Citron,177 M. Citterio,66a A. Clark,52 M. R. Clark,38 P. J. Clark,48 C. Clement,43a,43b Y. Coadou,99 M. Cobal,64a,64c A. Coccaro,53b J. Cochran,76 H. Cohen,158 A. E. C. Coimbra,177 L. Colasurdo,117 B. Cole,38 A. P. Colijn,118 J. Collot,56 P. Conde Muiño,137a,m E. Coniavitis,50 S. H. Connell,32b I. A. Connelly,98 S. Constantinescu,27b F. Conventi,67a,n A. M. Cooper-Sarkar,132 F. Cormier,172 K. J. R. Cormier,164 L. D. Corpe,92 M. Corradi,70a,70b E. E. Corrigan,94 F. Corriveau,101,o A. Cortes-Gonzalez,35 M. J. Costa,171 F. Costanza,5 D. Costanzo,146 G. Cottin,31 G. Cowan,91 J. W. Cowley,31 B. E. Cox,98 J. Crane,98 K. Cranmer,122 S. J. Crawley,55 R. A. Creager,134 G. Cree,33 S. Crépé-Renaudin,56 F. Crescioli,133 M. Cristinziani,24 V. Croft,122 G. Crosetti,40b,40a A. Cueto,96 T. Cuhadar Donszelmann,146 A. R. Cukierman,150 S. Czekierda,82 P. Czodrowski,35 M. J. Da Cunha Sargedas De Sousa,58b C. Da Via,98 W. Dabrowski,81a T. Dado,28a,p S. Dahbi,34e T. Dai,103 F. Dallaire,107 C. Dallapiccola,100 M. Dam,39 G. D’amen,23b,23a J. Damp,97 J. R. Dandoy,134 M. F. Daneri,30 N. P. Dang,178,g N. D Dann,98 M. Danninger,172 V. Dao,35 G. Darbo,53b S. Darmora,8 O. Dartsi,5 A. Dattagupta,128 T. Daubney,44 S. D’Auria,66a,66b W. Davey,24 C. David,44 T. Davidek,140 D. R. Davis,47 E. Dawe,102 I. Dawson,146 K. De,8 R. De Asmundis,67a A. De Benedetti,125 M. De Beurs,118 S. De Castro,23b,23a S. De Cecco,70a,70b N. De Groot,117 P. de Jong,118 H. De la Torre,104 F. De Lorenzi,76 A. De Maria,69a,69b D. De Pedis,70a A. De Salvo,70a U. De Sanctis,71a,71b M. De Santis,71a,71b A. De Santo,153 K. De Vasconcelos Corga,99 J. B. De Vivie De Regie,129 C. Debenedetti,143 D. V. Dedovich,77 N. Dehghanian,3 M. Del Gaudio,40b,40a J. Del Peso,96 Y. Delabat Diaz,44 D. Delgove,129 F. Deliot,142 C. M. Delitzsch,7 M. Della Pietra,67a,67b D. Della Volpe,52 A. Dell’Acqua,35 L. Dell’Asta,25 M. Delmastro,5 C. Delporte,129 P. A. Delsart,56 D. A. DeMarco,164 S. Demers,180 M. Demichev,77 S. P. Denisov,121 D. Denysiuk,118 L. D’Eramo,133 D. Derendarz,82 J. E. Derkaoui,34d F. Derue,133 P. Dervan,88 K. Desch,24 C. Deterre,44 K. Dette,164 M. R. Devesa,30 P. O. Deviveiros,35 A. Dewhurst,141 S. Dhaliwal,26 F. A. Di Bello,52 A. Di Ciaccio,71a,71b L. Di Ciaccio,5 W. K. Di Clemente,134 C. Di Donato,67a,67b 072009-26 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) A. Di Girolamo,35 G. Di Gregorio,69a,69b B. Di Micco,72a,72b R. Di Nardo,100 K. F. Di Petrillo,57 R. Di Sipio,164 D. Di Valentino,33 C. Diaconu,99 M. Diamond,164 F. A. Dias,39 T. Dias Do Vale,137a M. A. Diaz,144a J. Dickinson,18 E. B. Diehl,103 J. Dietrich,19 S. Díez Cornell,44 A. Dimitrievska,18 J. Dingfelder,24 F. Dittus,35 F. Djama,99 T. Djobava,156b J. I. Djuvsland,17 M. A. B. Do Vale,78c M. Dobre,27b D. Dodsworth,26 C. Doglioni,94 J. Dolejsi,140 Z. Dolezal,140 M. Donadelli,78d J. Donini,37 A. D’onofrio,90 M. D’Onofrio,88 J. Dopke,141 A. Doria,67a M. T. Dova,86 A. T. Doyle,55 E. Drechsler,149 E. Dreyer,149 T. Dreyer,51 Y. Du,58b F. Dubinin,108 M. Dubovsky,28a A. Dubreuil,52 E. Duchovni,177 G. Duckeck,112 A. Ducourthial,133 O. A. Ducu,107,q D. Duda,113 A. Dudarev,35 A. C. Dudder,97 E. M. Duffield,18 L. Duflot,129 M. Dührssen,35 C. Dülsen,179 M. Dumancic,177 A. E. Dumitriu,27b,r A. K. Duncan,55 M. Dunford,59a A. Duperrin,99 H. Duran Yildiz,4a M. Düren,54 A. Durglishvili,156b D. Duschinger,46 B. Dutta,44 D. Duvnjak,1 G. Dyckes,134 M. Dyndal,44 S. Dysch,98 B. S. Dziedzic,82 K. M. Ecker,113 R. C. Edgar,103 T. Eifert,35 G. Eigen,17 K. Einsweiler,18 T. Ekelof,169 M. El Kacimi,34c R. El Kosseifi,99 V. Ellajosyula,99 M. Ellert,169 F. Ellinghaus,179 A. A. Elliot,90 N. Ellis,35 J. Elmsheuser,29 M. Elsing,35 D. Emeliyanov,141 A. Emerman,38 Y. Enari,160 J. S. Ennis,175 M. B. Epland,47 J. Erdmann,45 A. Ereditato,20 S. Errede,170 M. Escalier,129 C. Escobar,171 O. Estrada Pastor,171 A. I. Etienvre,142 E. Etzion,158 H. Evans,63 A. Ezhilov,135 M. Ezzi,34e F. Fabbri,55 L. Fabbri,23b,23a V. Fabiani,117 G. Facini,92 R. M. Faisca Rodrigues Pereira,137a R. M. Fakhrutdinov,121 S. Falciano,70a P. J. Falke,5 S. Falke,5 J. Faltova,140 Y. Fang,15a M. Fanti,66a,66b A. Farbin,8 A. Farilla,72a E. M. Farina,68a,68b T. Farooque,104 S. Farrell,18 S. M. Farrington,175 P. Farthouat,35 F. Fassi,34e P. Fassnacht,35 D. Fassouliotis,9 M. Faucci Giannelli,48 W. J. Fawcett,31 L. Fayard,129 O. L. Fedin,135,s W. Fedorko,172 M. Feickert,41 S. Feigl,131 L. Feligioni,99 C. Feng,58b E. J. Feng,35 M. Feng,47 M. J. Fenton,55 A. B. Fenyuk,121 J. Ferrando,44 A. Ferrari,169 P. Ferrari,118 R. Ferrari,68a D. E. Ferreira de Lima,59b A. Ferrer,171 D. Ferrere,52 C. Ferretti,103 F. Fiedler,97 A. Filipčič,89 F. Filthaut,117 K. D. Finelli,25 M. C. N. Fiolhais,137a,137c,t L. Fiorini,171 C. Fischer,14 W. C. Fisher,104 N. Flaschel,44 I. Fleck,148 P. Fleischmann,103 R. R. M. Fletcher,134 T. Flick,179 B. M. Flierl,112 L. M. Flores,134 L. R. Flores Castillo,61a F. M. Follega,73a,73b N. Fomin,17 G. T. Forcolin,73a,73b A. Formica,142 F. A. Förster,14 A. C. Forti,98 A. G. Foster,21 D. Fournier,129 H. Fox,87 S. Fracchia,146 P. Francavilla,69a,69b M. Franchini,23b,23a S. Franchino,59a D. Francis,35 L. Franconi,143 M. Franklin,57 M. Frate,168 A. N. Fray,90 D. Freeborn,92 B. Freund,107 W. S. Freund,78b E. M. Freundlich,45 D. C. Frizzell,125 D. Froidevaux,35 J. A. Frost,132 C. Fukunaga,161 E. Fullana Torregrosa,171 E. Fumagalli,53b,53a T. Fusayasu,114 J. Fuster,171 O. Gabizon,157 A. Gabrielli,23b,23a A. Gabrielli,18 G. P. Gach,81a S. Gadatsch,52 P. Gadow,113 G. Gagliardi,53b,53a L. G. Gagnon,107 C. Galea,27b B. Galhardo,137a,137c E. J. Gallas,132 B. J. Gallop,141 P. Gallus,139 G. Galster,39 R. Gamboa Goni,90 K. K. Gan,123 S. Ganguly,177 J. Gao,58a Y. Gao,88 Y. S. Gao,150,u C. García,171 J. E. García Navarro,171 J. A. García Pascual,15a C. Garcia-Argos,50 M. Garcia-Sciveres,18 R. W. Gardner,36 N. Garelli,150 S. Gargiulo,50 V. Garonne,131 K. Gasnikova,44 A. Gaudiello,53b,53a G. Gaudio,68a I. L. Gavrilenko,108 A. Gavrilyuk,109 C. Gay,172 G. Gaycken,24 E. N. Gazis,10 C. N. P. Gee,141 J. Geisen,51 M. Geisen,97 M. P. Geisler,59a C. Gemme,53b M. H. Genest,56 C. Geng,103 S. Gentile,70a,70b S. George,91 D. Gerbaudo,14 G. Gessner,45 S. Ghasemi,148 M. Ghasemi Bostanabad,173 M. Ghneimat,24 B. Giacobbe,23b S. Giagu,70a,70b N. Giangiacomi,23b,23a P. Giannetti,69a A. Giannini,67a,67b S. M. Gibson,91 M. Gignac,143 D. Gillberg,33 G. Gilles,179 D. M. Gingrich,3,f M. P. Giordani,64a,64c F. M. Giorgi,23b P. F. Giraud,142 P. Giromini,57 G. Giugliarelli,64a,64c D. Giugni,66a F. Giuli,132 M. Giulini,59b S. Gkaitatzis,159 I. Gkialas,9,v E. L. Gkougkousis,14 P. Gkountoumis,10 L. K. Gladilin,111 C. Glasman,96 J. Glatzer,14 P. C. F. Glaysher,44 A. Glazov,44 M. Goblirsch-Kolb,26 J. Godlewski,82 S. Goldfarb,102 T. Golling,52 D. Golubkov,121 A. Gomes,137a,137b R. Goncalves Gama,51 R. Gonçalo,137a G. Gonella,50 L. Gonella,21 A. Gongadze,77 F. Gonnella,21 J. L. Gonski,57 S. González de la Hoz,171 S. Gonzalez-Sevilla,52 L. Goossens,35 P. A. Gorbounov,109 H. A. Gordon,29 B. Gorini,35 E. Gorini,65a,65b A. Gorišek,89 A. T. Goshaw,47 C. Gössling,45 M. I. Gostkin,77 C. A. Gottardo,24 C. R. Goudet,129 D. Goujdami,34c A. G. Goussiou,145 N. Govender,32b,w C. Goy,5 E. Gozani,157 I. Grabowska-Bold,81a P. O. J. Gradin,169 E. C. Graham,88 J. Gramling,168 E. Gramstad,131 S. Grancagnolo,19 V. Gratchev,135 P. M. Gravila,27f F. G. Gravili,65a,65b C. Gray,55 H. M. Gray,18 Z. D. Greenwood,93,x C. Grefe,24 K. Gregersen,94 I. M. Gregor,44 P. Grenier,150 K. Grevtsov,44 N. A. Grieser,125 J. Griffiths,8 A. A. Grillo,143 K. Grimm,150,y S. Grinstein,14,z Ph. Gris,37 J.-F. Grivaz,129 S. Groh,97 E. Gross,177 J. Grosse-Knetter,51 G. C. Grossi,93 Z. J. Grout,92 C. Grud,103 A. Grummer,116 L. Guan,103 W. Guan,178 J. Guenther,35 A. Guerguichon,129 F. Guescini,165a D. Guest,168 R. Gugel,50 B. Gui,123 T. Guillemin,5 S. Guindon,35 U. Gul,55 J. Guo,58c W. Guo,103 Y. Guo,58a,aa Z. Guo,99 R. Gupta,44 S. Gurbuz,12c G. Gustavino,125 P. Gutierrez,125 C. Gutschow,92 C. Guyot,142 M. P. Guzik,81a C. Gwenlan,132 C. B. Gwilliam,88 A. Haas,122 C. Haber,18 H. K. Hadavand,8 N. Haddad,34e A. Hadef,58a S. Hageböck,24 M. Hagihara,166 M. Haleem,174 J. Haley,126 G. Halladjian,104 G. D. Hallewell,99 072009-27 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) K. Hamacher,179 P. Hamal,127 K. Hamano,173 A. Hamilton,32a G. N. Hamity,146 K. Han,58a,bb L. Han,58a S. Han,15d K. Hanagaki,79,cc M. Hance,143 D. M. Handl,112 B. Haney,134 R. Hankache,133 P. Hanke,59a E. Hansen,94 J. B. Hansen,39 J. D. Hansen,39 M. C. Hansen,24 P. H. Hansen,39 K. Hara,166 A. S. Hard,178 T. Harenberg,179 S. Harkusha,105 P. F. Harrison,175 N. M. Hartmann,112 Y. Hasegawa,147 A. Hasib,48 S. Hassani,142 S. Haug,20 R. Hauser,104 L. Hauswald,46 L. B. Havener,38 M. Havranek,139 C. M. Hawkes,21 R. J. Hawkings,35 D. Hayden,104 C. Hayes,152 C. P. Hays,132 J. M. Hays,90 H. S. Hayward,88 S. J. Haywood,141 F. He,58a M. P. Heath,48 V. Hedberg,94 L. Heelan,8 S. Heer,24 K. K. Heidegger,50 J. Heilman,33 S. Heim,44 T. Heim,18 B. Heinemann,44,dd J. J. Heinrich,112 L. Heinrich,122 C. Heinz,54 J. Hejbal,138 L. Helary,35 A. Held,172 S. Hellesund,131 C. M. Helling,143 S. Hellman,43a,43b C. Helsens,35 R. C. W. Henderson,87 Y. Heng,178 S. Henkelmann,172 A. M. Henriques Correia,35 G. H. Herbert,19 H. Herde,26 V. Herget,174 Y. Hernández Jiménez,32c H. Herr,97 M. G. Herrmann,112 T. Herrmann,46 G. Herten,50 R. Hertenberger,112 L. Hervas,35 T. C. Herwig,134 G. G. Hesketh,92 N. P. Hessey,165a A. Higashida,160 S. Higashino,79 E. Higón-Rodriguez,171 K. Hildebrand,36 E. Hill,173 J. C. Hill,31 K. K. Hill,29 K. H. Hiller,44 S. J. Hillier,21 M. Hils,46 I. Hinchliffe,18 F. Hinterkeuser,24 M. Hirose,130 D. Hirschbuehl,179 B. Hiti,89 O. Hladik,138 D. R. Hlaluku,32c X. Hoad,48 J. Hobbs,152 N. Hod,165a M. C. Hodgkinson,146 A. Hoecker,35 M. R. Hoeferkamp,116 F. Hoenig,112 D. Hohn,50 D. Hohov,129 T. R. Holmes,36 M. Holzbock,112 M. Homann,45 B. H. Hommels,31 S. Honda,166 T. Honda,79 T. M. Hong,136 A. Hönle,113 B. H. Hooberman,170 W. H. Hopkins,128 Y. Horii,115 P. Horn,46 A. J. Horton,149 L. A. Horyn,36 J-Y. Hostachy,56 A. Hostiuc,145 S. Hou,155 A. Hoummada,34a J. Howarth,98 J. Hoya,86 M. Hrabovsky,127 J. Hrdinka,35 I. Hristova,19 J. Hrivnac,129 A. Hrynevich,106 T. Hryn’ova,5 P. J. Hsu,62 S.-C. Hsu,145 Q. Hu,29 S. Hu,58c Y. Huang,15a Z. Hubacek,139 F. Hubaut,99 M. Huebner,24 F. Huegging,24 T. B. Huffman,132 M. Huhtinen,35 R. F. H. Hunter,33 P. Huo,152 A. M. Hupe,33 N. Huseynov,77,e J. Huston,104 J. Huth,57 R. Hyneman,103 G. Iacobucci,52 G. Iakovidis,29 I. Ibragimov,148 L. Iconomidou-Fayard,129 Z. Idrissi,34e P. Iengo,35 R. Ignazzi,39 O. Igonkina,118,ee R. Iguchi,160 T. Iizawa,52 Y. Ikegami,79 M. Ikeno,79 D. Iliadis,159 N. Ilic,117 F. Iltzsche,46 G. Introzzi,68a,68b M. Iodice,72a K. Iordanidou,38 V. Ippolito,70a,70b M. F. Isacson,169 N. Ishijima,130 M. Ishino,160 M. Ishitsuka,162 W. Islam,126 C. Issever,132 S. Istin,157 F. Ito,166 J. M. Iturbe Ponce,61a R. Iuppa,73a,73b A. Ivina,177 H. Iwasaki,79 J. M. Izen,42 V. Izzo,67a P. Jacka,138 P. Jackson,1 R. M. Jacobs,24 V. Jain,2 G. Jäkel,179 K. B. Jakobi,97 K. Jakobs,50 S. Jakobsen,74 T. Jakoubek,138 D. O. Jamin,126 R. Jansky,52 J. Janssen,24 M. Janus,51 P. A. Janus,81a G. Jarlskog,94 N. Javadov,77,e T. Javůrek,35 M. Javurkova,50 F. Jeanneau,142 L. Jeanty,18 J. Jejelava,156a,ff A. Jelinskas,175 P. Jenni,50,gg J. Jeong,44 N. Jeong,44 S. Jézéquel,5 H. Ji,178 J. Jia,152 H. Jiang,76 Y. Jiang,58a Z. Jiang,150,hh S. Jiggins,50 F. A. Jimenez Morales,37 J. Jimenez Pena,171 S. Jin,15c A. Jinaru,27b O. Jinnouchi,162 H. Jivan,32c P. Johansson,146 K. A. Johns,7 C. A. Johnson,63 K. Jon-And,43a,43b R. W. L. Jones,87 S. D. Jones,153 S. Jones,7 T. J. Jones,88 J. Jongmanns,59a P. M. Jorge,137a,137b J. Jovicevic,165a X. Ju,18 J. J. Junggeburth,113 A. Juste Rozas,14,z A. Kaczmarska,82 M. Kado,129 H. Kagan,123 M. Kagan,150 T. Kaji,176 E. Kajomovitz,157 C. W. Kalderon,94 A. Kaluza,97 S. Kama,41 A. Kamenshchikov,121 L. Kanjir,89 Y. Kano,160 V. A. Kantserov,110 J. Kanzaki,79 L. S. Kaplan,178 D. Kar,32c M. J. Kareem,165b E. Karentzos,10 S. N. Karpov,77 Z. M. Karpova,77 V. Kartvelishvili,87 A. N. Karyukhin,121 L. Kashif,178 R. D. Kass,123 A. Kastanas,43a,43b Y. Kataoka,160 C. Kato,58d,58c J. Katzy,44 K. Kawade,80 K. Kawagoe,85 T. Kawaguchi,115 T. Kawamoto,160 G. Kawamura,51 E. F. Kay,88 V. F. Kazanin,120b,120a R. Keeler,173 R. Kehoe,41 J. S. Keller,33 E. Kellermann,94 J. J. Kempster,21 J. Kendrick,21 O. Kepka,138 S. Kersten,179 B. P. Kerševan,89 S. Ketabchi Haghighat,164 R. A. Keyes,101 M. Khader,170 F. Khalil-Zada,13 A. Khanov,126 A. G. Kharlamov,120b,120a T. Kharlamova,120b,120a E. E. Khoda,172 A. Khodinov,163 T. J. Khoo,52 E. Khramov,77 J. Khubua,156b S. Kido,80 M. Kiehn,52 C. R. Kilby,91 Y. K. Kim,36 N. Kimura,64a,64c O. M. Kind,19 B. T. King,88 D. Kirchmeier,46 J. Kirk,141 A. E. Kiryunin,113 T. Kishimoto,160 D. Kisielewska,81a V. Kitali,44 O. Kivernyk,5 E. Kladiva,28b,a T. Klapdor-Kleingrothaus,50 M. H. Klein,103 M. Klein,88 U. Klein,88 K. Kleinknecht,97 P. Klimek,119 A. Klimentov,29 T. Klingl,24 T. Klioutchnikova,35 F. F. Klitzner,112 P. Kluit,118 S. Kluth,113 E. Kneringer,74 E. B. F. G. Knoops,99 A. Knue,50 A. Kobayashi,160 D. Kobayashi,85 T. Kobayashi,160 M. Kobel,46 M. Kocian,150 P. Kodys,140 P. T. Koenig,24 T. Koffas,33 E. Koffeman,118 N. M. Köhler,113 T. Koi,150 M. Kolb,59b I. Koletsou,5 T. Kondo,79 N. Kondrashova,58c K. Köneke,50 A. C. König,117 T. Kono,79 R. Konoplich,122,ii V. Konstantinides,92 N. Konstantinidis,92 B. Konya,94 R. Kopeliansky,63 S. Koperny,81a K. Korcyl,82 K. Kordas,159 G. Koren,158 A. Korn,92 I. Korolkov,14 E. V. Korolkova,146 N. Korotkova,111 O. Kortner,113 S. Kortner,113 T. Kosek,140 V. V. Kostyukhin,24 A. Kotwal,47 A. Koulouris,10 A. Kourkoumeli-Charalampidi,68a,68b C. Kourkoumelis,9 E. Kourlitis,146 V. Kouskoura,29 A. B. Kowalewska,82 R. Kowalewski,173 T. Z. Kowalski,81a C. Kozakai,160 W. Kozanecki,142 A. S. Kozhin,121 V. A. Kramarenko,111 G. Kramberger,89 D. Krasnopevtsev,58a M. W. Krasny,133 A. Krasznahorkay,35 D. Krauss,113 J. A. Kremer,81a 072009-28 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) J. Kretzschmar,88 P. Krieger,164 K. Krizka,18 K. Kroeninger,45 H. Kroha,113 J. Kroll,138 J. Kroll,134 J. Krstic,16 U. Kruchonak,77 H. Krüger,24 N. Krumnack,76 M. C. Kruse,47 T. Kubota,102 S. Kuday,4b J. T. Kuechler,179 S. Kuehn,35 A. Kugel,59a T. Kuhl,44 V. Kukhtin,77 R. Kukla,99 Y. Kulchitsky,105,jj S. Kuleshov,144b Y. P. Kulinich,170 M. Kuna,56 T. Kunigo,83 A. Kupco,138 T. Kupfer,45 O. Kuprash,158 H. Kurashige,80 L. L. Kurchaninov,165a Y. A. Kurochkin,105 A. Kurova,110 M. G. Kurth,15d E. S. Kuwertz,35 M. Kuze,162 J. Kvita,127 T. Kwan,101 A. La Rosa,113 J. L. La Rosa Navarro,78d L. La Rotonda,40b,40a F. La Ruffa,40b,40a C. Lacasta,171 F. Lacava,70a,70b J. Lacey,44 D. P. J. Lack,98 H. Lacker,19 D. Lacour,133 E. Ladygin,77 R. Lafaye,5 B. Laforge,133 T. Lagouri,32c S. Lai,51 S. Lammers,63 W. Lampl,7 E. Lançon,29 U. Landgraf,50 M. P. J. Landon,90 M. C. Lanfermann,52 V. S. Lang,44 J. C. Lange,51 R. J. Langenberg,35 A. J. Lankford,168 F. Lanni,29 K. Lantzsch,24 A. Lanza,68a A. Lapertosa,53b,53a S. Laplace,133 J. F. Laporte,142 T. Lari,66a F. Lasagni Manghi,23b,23a M. Lassnig,35 T. S. Lau,61a A. Laudrain,129 M. Lavorgna,67a,67b M. Lazzaroni,66a,66b B. Le,102 O. Le Dortz,133 E. Le Guirriec,99 E. P. Le Quilleuc,142 M. LeBlanc,7 T. LeCompte,6 F. Ledroit-Guillon,56 C. A. Lee,29 G. R. Lee,144a L. Lee,57 S. C. Lee,155 B. Lefebvre,101 M. Lefebvre,173 F. Legger,112 C. Leggett,18 K. Lehmann,149 N. Lehmann,179 G. Lehmann Miotto,35 W. A. Leight,44 A. Leisos,159,kk M. A. L. Leite,78d R. Leitner,140 D. Lellouch,177 K. J. C. Leney,92 T. Lenz,24 B. Lenzi,35 R. Leone,7 S. Leone,69a C. Leonidopoulos,48 G. Lerner,153 C. Leroy,107 R. Les,164 A. A. J. Lesage,142 C. G. Lester,31 M. Levchenko,135 J. Levêque,5 D. Levin,103 L. J. Levinson,177 D. Lewis,90 B. Li,15b B. Li,103 C-Q. Li,58a,ll H. Li,58a H. Li,58b K. Li,150 L. Li,58c M. Li,15a Q. Li,15d Q. Y. Li,58a S. Li,58d,58c X. Li,58c Y. Li,148 Z. Liang,15a B. Liberti,71a A. Liblong,164 K. Lie,61c S. Liem,118 A. Limosani,154 C. Y. Lin,31 K. Lin,104 T. H. Lin,97 R. A. Linck,63 J. H. Lindon,21 B. E. Lindquist,152 A. L. Lionti,52 E. Lipeles,134 A. Lipniacka,17 M. Lisovyi,59b T. M. Liss,170,mm A. Lister,172 A. M. Litke,143 J. D. Little,8 B. Liu,76 B. L Liu,6 H. B. Liu,29 H. Liu,103 J. B. Liu,58a J. K. K. Liu,132 K. Liu,133 M. Liu,58a P. Liu,18 Y. Liu,15a Y. L. Liu,58a Y. W. Liu,58a M. Livan,68a,68b A. Lleres,56 J. Llorente Merino,15a S. L. Lloyd,90 C. Y. Lo,61b F. Lo Sterzo,41 E. M. Lobodzinska,44 P. Loch,7 T. Lohse,19 K. Lohwasser,146 M. Lokajicek,138 J. D. Long,170 R. E. Long,87 L. Longo,65a,65b K. A. Looper,123 J. A. Lopez,144b I. Lopez Paz,98 A. Lopez Solis,146 J. Lorenz,112 N. Lorenzo Martinez,5 M. Losada,22 P. J. Lösel,112 A. Lösle,50 X. Lou,44 X. Lou,15a A. Lounis,129 J. Love,6 P. A. Love,87 J. J. Lozano Bahilo,171 H. Lu,61a M. Lu,58a Y. J. Lu,62 H. J. Lubatti,145 C. Luci,70a,70b A. Lucotte,56 C. Luedtke,50 F. Luehring,63 I. Luise,133 L. Luminari,70a B. Lund-Jensen,151 M. S. Lutz,100 P. M. Luzi,133 D. Lynn,29 R. Lysak,138 E. Lytken,94 F. Lyu,15a V. Lyubushkin,77 T. Lyubushkina,77 H. Ma,29 L. L. Ma,58b Y. Ma,58b G. Maccarrone,49 A. Macchiolo,113 C. M. Macdonald,146 J. Machado Miguens,134,137b D. Madaffari,171 R. Madar,37 W. F. Mader,46 N. Madysa,46 J. Maeda,80 K. Maekawa,160 S. Maeland,17 T. Maeno,29 M. Maerker,46 A. S. Maevskiy,111 V. Magerl,50 D. J. Mahon,38 C. Maidantchik,78b T. Maier,112 A. Maio,137a,137b,137d O. Majersky,28a S. Majewski,128 Y. Makida,79 N. Makovec,129 B. Malaescu,133 Pa. Malecki,82 V. P. Maleev,135 F. Malek,56 U. Mallik,75 D. Malon,6 C. Malone,31 S. Maltezos,10 S. Malyukov,35 J. Mamuzic,171 G. Mancini,49 I. Mandić,89 J. Maneira,137a L. Manhaes de Andrade Filho,78a J. Manjarres Ramos,46 K. H. Mankinen,94 A. Mann,112 A. Manousos,74 B. Mansoulie,142 S. Manzoni,66a,66b A. Marantis,159 G. Marceca,30 L. March,52 L. Marchese,132 G. Marchiori,133 M. Marcisovsky,138 C. Marcon,94 C. A. Marin Tobon,35 M. Marjanovic,37 F. Marroquim,78b Z. Marshall,18 M. U. F Martensson,169 S. Marti-Garcia,171 C. B. Martin,123 T. A. Martin,175 V. J. Martin,48 B. Martin dit Latour,17 M. Martinez,14,z V. I. Martinez Outschoorn,100 S. Martin-Haugh,141 V. S. Martoiu,27b A. C. Martyniuk,92 A. Marzin,35 L. Masetti,97 T. Mashimo,160 R. Mashinistov,108 J. Masik,98 A. L. Maslennikov,120b,120a L. H. Mason,102 L. Massa,71a,71b P. Massarotti,67a,67b P. Mastrandrea,152 A. Mastroberardino,40b,40a T. Masubuchi,160 P. Mättig,24 J. Maurer,27b B. Maček,89 S. J. Maxfield,88 D. A. Maximov,120b,120a R. Mazini,155 I. Maznas,159 S. M. Mazza,143 S. P. Mc Kee,103 A. McCarn,41 T. G. McCarthy,113 L. I. McClymont,92 W. P. McCormack,18 E. F. McDonald,102 J. A. Mcfayden,35 G. Mchedlidze,51 M. A. McKay,41 K. D. McLean,173 S. J. McMahon,141 P. C. McNamara,102 C. J. McNicol,175 R. A. McPherson,173,o J. E. Mdhluli,32c Z. A. Meadows,100 S. Meehan,145 T. M. Megy,50 S. Mehlhase,112 A. Mehta,88 T. Meideck,56 B. Meirose,42 D. Melini,171,nn B. R. Mellado Garcia,32c J. D. Mellenthin,51 M. Melo,28a F. Meloni,44 A. Melzer,24 S. B. Menary,98 E. D. Mendes Gouveia,137a L. Meng,88 X. T. Meng,103 S. Menke,113 E. Meoni,40b,40a S. Mergelmeyer,19 S. A. M. Merkt,136 C. Merlassino,20 P. Mermod,52 L. Merola,67a,67b C. Meroni,66a F. S. Merritt,36 A. Messina,70a,70b J. Metcalfe,6 A. S. Mete,168 C. Meyer,63 J. Meyer,157 J-P. Meyer,142 H. Meyer Zu Theenhausen,59a F. Miano,153 R. P. Middleton,141 L. Mijović,48 G. Mikenberg,177 M. Mikestikova,138 M. Mikuž,89 M. Milesi,102 A. Milic,164 D. A. Millar,90 D. W. Miller,36 A. Milov,177 D. A. Milstead,43a,43b R. A. Mina,150,hh A. A. Minaenko,121 M. Miñano Moya,171 I. A. Minashvili,156b A. I. Mincer,122 B. Mindur,81a M. Mineev,77 Y. Minegishi,160 Y. Ming,178 L. M. Mir,14 A. Mirto,65a,65b K. P. Mistry,134 T. Mitani,176 J. Mitrevski,112 V. A. Mitsou,171 M. Mittal,58c A. Miucci,20 P. S. Miyagawa,146 A. Mizukami,79 J. U. Mjörnmark,94 072009-29 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) T. Mkrtchyan,181 M. Mlynarikova,140 T. Moa,43a,43b K. Mochizuki,107 P. Mogg,50 S. Mohapatra,38 S. Molander,43a,43b R. Moles-Valls,24 M. C. Mondragon,104 K. Mönig,44 J. Monk,39 E. Monnier,99 A. Montalbano,149 J. Montejo Berlingen,35 F. Monticelli,86 S. Monzani,66a N. Morange,129 D. Moreno,22 M. Moreno Llácer,35 P. Morettini,53b M. Morgenstern,118 S. Morgenstern,46 D. Mori,149 M. Morii,57 M. Morinaga,176 V. Morisbak,131 A. K. Morley,35 G. 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Y. Ng,61c Y. S. Ng,19 Y. W. Y. Ng,168 H. D. N. Nguyen,99 T. Nguyen Manh,107 E. Nibigira,37 R. B. Nickerson,132 R. Nicolaidou,142 D. S. Nielsen,39 J. Nielsen,143 N. Nikiforou,11 V. Nikolaenko,121,pp I. Nikolic-Audit,133 K. Nikolopoulos,21 P. Nilsson,29 H. R. Nindhito,52 Y. Ninomiya,79 A. Nisati,70a N. Nishu,58c R. Nisius,113 I. Nitsche,45 T. Nitta,176 T. Nobe,160 Y. Noguchi,83 M. Nomachi,130 I. Nomidis,133 M. A. Nomura,29 T. Nooney,90 M. Nordberg,35 N. Norjoharuddeen,132 T. Novak,89 O. Novgorodova,46 R. Novotny,139 L. Nozka,127 K. Ntekas,168 E. Nurse,92 F. Nuti,102 F. G. Oakham,33,f H. Oberlack,113 J. Ocariz,133 A. Ochi,80 I. Ochoa,38 J. P. Ochoa-Ricoux,144a K. O’Connor,26 S. Oda,85 S. Odaka,79 S. Oerdek,51 A. Oh,98 S. H. Oh,47 C. C. Ohm,151 H. Oide,53b,53a M. L. Ojeda,164 H. Okawa,166 Y. Okazaki,83 Y. Okumura,160 T. Okuyama,79 A. Olariu,27b L. F. Oleiro Seabra,137a S. A. Olivares Pino,144a D. Oliveira Damazio,29 J. L. Oliver,1 M. J. R. Olsson,36 A. Olszewski,82 J. Olszowska,82 D. C. O’Neil,149 A. Onofre,137a,137e K. Onogi,115 P. U. E. Onyisi,11 H. Oppen,131 M. J. Oreglia,36 G. E. Orellana,86 Y. Oren,158 D. Orestano,72a,72b E. C. Orgill,98 N. Orlando,61b A. A. O’Rourke,44 R. S. Orr,164 B. Osculati,53b,53a,a V. O’Shea,55 R. Ospanov,58a G. Otero y Garzon,30 H. Otono,85 M. Ouchrif,34d F. Ould-Saada,131 A. Ouraou,142 Q. Ouyang,15a M. Owen,55 R. E. Owen,21 V. E. Ozcan,12c N. Ozturk,8 J. Pacalt,127 H. A. Pacey,31 K. Pachal,149 A. Pacheco Pages,14 L. Pacheco Rodriguez,142 C. Padilla Aranda,14 S. Pagan Griso,18 M. Paganini,180 G. Palacino,63 S. Palazzo,48 S. Palestini,35 M. Palka,81b D. Pallin,37 I. Panagoulias,10 C. E. Pandini,35 J. G. Panduro Vazquez,91 P. Pani,35 G. Panizzo,64a,64c L. Paolozzi,52 T. D. Papadopoulou,10 K. Papageorgiou,9,v A. Paramonov,6 D. Paredes Hernandez,61b S. R. Paredes Saenz,132 B. Parida,163 T. H. Park,33 A. J. Parker,87 K. A. Parker,44 M. A. Parker,31 F. Parodi,53b,53a J. A. Parsons,38 U. Parzefall,50 V. R. Pascuzzi,164 J. M. P. Pasner,143 E. Pasqualucci,70a S. Passaggio,53b F. Pastore,91 P. Pasuwan,43a,43b S. Pataraia,97 J. R. Pater,98 A. Pathak,178,g T. Pauly,35 B. Pearson,113 M. Pedersen,131 L. Pedraza Diaz,117 R. Pedro,137a,137b S. V. Peleganchuk,120b,120a O. Penc,138 C. Peng,15d H. Peng,58a B. S. Peralva,78a M. M. Perego,129 A. P. Pereira Peixoto,137a D. V. Perepelitsa,29 F. Peri,19 L. Perini,66a,66b H. Pernegger,35 S. Perrella,67a,67b V. D. Peshekhonov,77,a K. Peters,44 R. F. Y. Peters,98 B. A. Petersen,35 T. C. Petersen,39 E. Petit,56 A. Petridis,1 C. Petridou,159 P. Petroff,129 M. Petrov,132 F. Petrucci,72a,72b M. Pettee,180 N. E. Pettersson,100 A. Peyaud,142 R. Pezoa,144b T. Pham,102 F. H. Phillips,104 P. W. Phillips,141 M. W. Phipps,170 G. Piacquadio,152 E. Pianori,18 A. Picazio,100 R. H. Pickles,98 R. Piegaia,30 J. E. Pilcher,36 A. D. Pilkington,98 M. Pinamonti,71a,71b J. L. Pinfold,3 M. Pitt,177 L. Pizzimento,71a,71b M.-A. Pleier,29 V. Pleskot,140 E. Plotnikova,77 D. Pluth,76 P. Podberezko,120b,120a R. 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Zwalinski35 (ATLAS Collaboration) 1 Department of Physics, University of Adelaide, Adelaide, Australia 2 Physics Department, SUNY Albany, Albany, New York, USA 3 Department of Physics, University of Alberta, Edmonton, Alberta, Canada 4a Department of Physics, Ankara University, Ankara, Turkey 4b Istanbul Aydin University, Istanbul, Turkey 4c 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, Illinois, USA 7 Department of Physics, University of Arizona, Tucson, Arizona, USA 8 Department of Physics, University of Texas at Arlington, Arlington, Texas, USA 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, Texas, USA 12a Bahcesehir University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey 12b Istanbul Bilgi University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey 12c Department of Physics, Bogazici University, Istanbul, Turkey 12d 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 15a Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China 15b Physics Department, Tsinghua University, Beijing, China 15c Department of Physics, Nanjing University, Nanjing, China 15d 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, California, USA 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 Centro de Investigaciónes, Universidad Antonio Nariño, Bogota, Colombia 23a Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna, Italy 23b INFN Sezione di Bologna, Italy 24 Physikalisches Institut, Universität Bonn, Bonn, Germany 25 Department of Physics, Boston University, Boston, Massachusetts, USA 26 Department of Physics, Brandeis University, Waltham, Massachusetts, USA 27a Transilvania University of Brasov, Brasov, Romania 27b Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania 27c Department of Physics, Alexandru Ioan Cuza University of Iasi, Iasi, Romania 27d National Institute for Research and Development of Isotopic and Molecular Technologies, Physics Department, Cluj-Napoca, Romania 072009-33 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) 27e University Politehnica Bucharest, Bucharest, Romania 27f West University in Timisoara, Timisoara, Romania 28a Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovak Republic 28b Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic 29 Physics Department, Brookhaven National Laboratory, Upton, New York, USA 30 Departamento de Física, Universidad de Buenos Aires, Buenos Aires, Argentina 31 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 32a Department of Physics, University of Cape Town, Cape Town, South Africa 32b Department of Mechanical Engineering Science, University of Johannesburg, Johannesburg, South Africa 32c School of Physics, University of the Witwatersrand, Johannesburg, South Africa 33 Department of Physics, Carleton University, Ottawa, Ontario, Canada 34a Faculté des Sciences Ain Chock, Réseau Universitaire de Physique des Hautes Energies—Université Hassan II, Casablanca, Morocco 34b Centre National de l’Energie des Sciences Techniques Nucleaires (CNESTEN), Rabat, Morocco 34c Faculté des Sciences Semlalia, Université Cadi Ayyad, LPHEA-Marrakech, Morocco 34d Faculté des Sciences, Université Mohamed Premier and LPTPM, Oujda, Morocco 34e Faculté des sciences, Université Mohammed V, Rabat, Morocco 35 CERN, Geneva, Switzerland 36 Enrico Fermi Institute, University of Chicago, Chicago Illinois, USA 37 LPC, Université Clermont Auvergne, CNRS/IN2P3, Clermont-Ferrand, France 38 Nevis Laboratory, Columbia University, Irvington, New York, USA 39 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark 40a Dipartimento di Fisica, Università della Calabria, Rende, Italy 40b INFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati, Italy 41 Physics Department, Southern Methodist University, Dallas, Texas, USA 42 Physics Department, University of Texas at Dallas, Richardson, Texas, USA 43a Department of Physics, Stockholm University, Sweden 43b Oskar Klein Centre, Stockholm, Sweden 44 Deutsches Elektronen-Synchrotron DESY, Hamburg and Zeuthen, Germany 45 Lehrstuhl für Experimentelle Physik IV, Technische Universität Dortmund, Dortmund, Germany 46 Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany 47 Department of Physics, Duke University, Durham, North Carolina, USA 48 SUPA—School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 49 INFN e Laboratori Nazionali di Frascati, Frascati, Italy 50 Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany 51 II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany 52 Département de Physique Nucléaire et Corpusculaire, Université de Genève, Genève, Switzerland 53a Dipartimento di Fisica, Università di Genova, Genova, Italy 53b INFN Sezione di Genova, Italy 54 II. Physikalisches Institut, Justus-Liebig-Universität Giessen, Giessen, Germany 55 SUPA—School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 56 LPSC, Université Grenoble Alpes, CNRS/IN2P3, Grenoble INP, Grenoble, France 57 Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, Massachusetts, USA 58a Department of Modern Physics and State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, China 58b Institute of Frontier and Interdisciplinary Science and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Qingdao, China 58c School of Physics and Astronomy, Shanghai Jiao Tong University, KLPPAC-MoE, SKLPPC, Shanghai, China 58d Tsung-Dao Lee Institute, Shanghai, China 59a Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 59b Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 60 Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan 61a Department of Physics, Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China 61b Department of Physics, University of Hong Kong, Hong Kong, China 61c Department of Physics and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China 62 Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 072009-34 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) 63 Department of Physics, Indiana University, Bloomington, Indiana, USA 64a INFN Gruppo Collegato di Udine, Sezione di Trieste, Udine, Italy 64b ICTP, Trieste, Italy 64c Dipartimento di Chimica, Fisica e Ambiente, Università di Udine, Udine, Italy 65a INFN Sezione di Lecce, Italy 65b Dipartimento di Matematica e Fisica, Università del Salento, Lecce, Italy 66a INFN Sezione di Milano, Italy 66b Dipartimento di Fisica, Università di Milano, Milano, Italy 67a INFN Sezione di Napoli, Italy 67b Dipartimento di Fisica, Università di Napoli, Napoli, Italy 68a INFN Sezione di Pavia, Italy 68b Dipartimento di Fisica, Università di Pavia, Pavia, Italy 69a INFN Sezione di Pisa, Italy 69b Dipartimento di Fisica E. Fermi, Università di Pisa, Pisa, Italy 70a INFN Sezione di Roma, Italy 70b Dipartimento di Fisica, Sapienza Università di Roma, Roma, Italy 71a INFN Sezione di Roma Tor Vergata, Italy 71b Dipartimento di Fisica, Università di Roma Tor Vergata, Roma, Italy 72a INFN Sezione di Roma Tre, Italy 72b Dipartimento di Matematica e Fisica, Università Roma Tre, Roma, Italy 73a INFN-TIFPA, Italy 73b Università degli Studi di Trento, Trento, Italy 74 Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität, Innsbruck, Austria 75 University of Iowa, Iowa City, Iowa, USA 76 Department of Physics and Astronomy, Iowa State University, Ames, Iowa, USA 77 Joint Institute for Nuclear Research, Dubna, Russia 78a Departamento de Engenharia Elétrica, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, Brazil 78b Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro, Brazil 78c Universidade Federal de São João del Rei (UFSJ), São João del Rei, Brazil 78d Instituto de Física, Universidade de São Paulo, São Paulo, Brazil 79 KEK, High Energy Accelerator Research Organization, Tsukuba, Japan 80 Graduate School of Science, Kobe University, Kobe, Japan 81a AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow, Poland 81b Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland 82 Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland 83 Faculty of Science, Kyoto University, Kyoto, Japan 84 Kyoto University of Education, Kyoto, Japan 85 Research Center for Advanced Particle Physics and Department of Physics, Kyushu University, Fukuoka, Japan 86 Instituto de Física La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina 87 Physics Department, Lancaster University, Lancaster, United Kingdom 88 Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 89 Department of Experimental Particle Physics, Jožef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana, Slovenia 90 School of Physics and Astronomy, Queen Mary University of London, London, United Kingdom 91 Department of Physics, Royal Holloway University of London, Egham, United Kingdom 92 Department of Physics and Astronomy, University College London, London, United Kingdom 93 Louisiana Tech University, Ruston, Los Angeles, USA 94 Fysiska institutionen, Lunds universitet, Lund, Sweden 95 Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), Villeurbanne, France 96 Departamento de Física Teorica C-15 and CIAFF, Universidad Autónoma de Madrid, Madrid, Spain 97 Institut für Physik, Universität Mainz, Mainz, Germany 98 School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 99 CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France 100 Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA 101 Department of Physics, McGill University, Montreal, Quebec, Canada 102 School of Physics, University of Melbourne, Victoria, Australia 072009-35 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) 103 Department of Physics, University of Michigan, Ann Arbor, Michigan, USA 104 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, USA 105 B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Belarus 106 Research Institute for Nuclear Problems of Byelorussian State University, Minsk, Belarus 107 Group of Particle Physics, University of Montreal, Montreal, Quebec, Canada 108 P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia 109 Institute for Theoretical and Experimental Physics of the National Research Centre Kurchatov Institute, Moscow, Russia 110 National Research Nuclear University MEPhI, Moscow, Russia 111 D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia 112 Fakultät für Physik, Ludwig-Maximilians-Universität München, München, Germany 113 Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany 114 Nagasaki Institute of Applied Science, Nagasaki, Japan 115 Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan 116 Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico, USA 117 Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands 118 Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, Netherlands 119 Department of Physics, Northern Illinois University, DeKalb, Illinois, USA 120a Budker Institute of Nuclear Physics and NSU, SB RAS, Novosibirsk, Russia 120b Novosibirsk State University Novosibirsk, Russia 121 Institute for High Energy Physics of the National Research Centre Kurchatov Institute, Protvino, Russia 122 Department of Physics, New York University, New York, New York, USA 123 Ohio State University, Columbus, Ohio, USA 124 Faculty of Science, Okayama University, Okayama, Japan 125 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, USA 126 Department of Physics, Oklahoma State University, Stillwater, Oklahoma, USA 127 Palacký University, RCPTM, Joint Laboratory of Optics, Olomouc, Czech Republic 128 Center for High Energy Physics, University of Oregon, Eugene, Oregon, USA 129 LAL, Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France 130 Graduate School of Science, Osaka University, Osaka, Japan 131 Department of Physics, University of Oslo, Oslo, Norway 132 Department of Physics, Oxford University, Oxford, United Kingdom 133 LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3, Paris, France 134 Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania, USA 135 Konstantinov Nuclear Physics Institute of National Research Centre “Kurchatov Institute”, PNPI, St. Petersburg, Russia 136 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania, USA 137a Laboratório de Instrumentação e Física Experimental de Partículas—LIP, Portugal 137b Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 137c Departamento de Física, Universidade de Coimbra, Coimbra, Portugal 137d Centro de Física Nuclear da Universidade de Lisboa, Lisboa, Portugal 137e Departamento de Física, Universidade do Minho, Braga, Portugal 137f Departamento de Física Teorica y del Cosmos, Universidad de Granada, Granada (Spain), Spain 137g Dep Física and CEFITEC of Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal 138 Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic 139 Czech Technical University in Prague, Prague, Czech Republic 140 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic 141 Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom 142 IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France 143 Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, California, USA 144a Departamento de Física, Pontificia Universidad Católica de Chile, Santiago, Chile 144b Departamento de Física, Universidad Técnica Federico Santa María, Valparaíso, Chile 145 Department of Physics, University of Washington, Seattle, Washington, USA 146 Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 147 Department of Physics, Shinshu University, Nagano, Japan 072009-36 MEASUREMENT OF THE tt̄Z AND tt̄W … PHYS. REV. D 99, 072009 (2019) 148 Department Physik, Universität Siegen, Siegen, Germany 149 Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada 150 SLAC National Accelerator Laboratory, Stanford, California, USA 151 Physics Department, Royal Institute of Technology, Stockholm, Sweden 152 Departments of Physics and Astronomy, Stony Brook University, Stony Brook, New York, USA 153 Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom 154 School of Physics, University of Sydney, Sydney, Australia 155 Institute of Physics, Academia Sinica, Taipei, Taiwan 156a E. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi, Georgia 156b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia 157 Department of Physics, Technion, Israel Institute of Technology, Haifa, Israel 158 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel 159 Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 160 International Center for Elementary Particle Physics and Department of Physics, University of Tokyo, Tokyo, Japan 161 Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan 162 Department of Physics, Tokyo Institute of Technology, Tokyo, Japan 163 Tomsk State University, Tomsk, Russia 164 Department of Physics, University of Toronto, Toronto, Ontario, Canada 165a TRIUMF, Vancouver, British Columbia, Canada 165b Department of Physics and Astronomy, York University, Toronto, Ontario, Canada 166 Division of Physics and Tomonaga Center for the History of the Universe, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Japan 167 Department of Physics and Astronomy, Tufts University, Medford, Massachusetts, USA 168 Department of Physics and Astronomy, University of California Irvine, Irvine, California, USA 169 Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden 170 Department of Physics, University of Illinois, Urbana, Illinois, USA 171 Instituto de Física Corpuscular (IFIC), Centro Mixto Universidad de Valencia—CSIC, Valencia, Spain 172 Department of Physics, University of British Columbia, Vancouver, British Columbia, Canada 173 Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada 174 Fakultät für Physik und Astronomie, Julius-Maximilians-Universität Würzburg, Würzburg, Germany 175 Department of Physics, University of Warwick, Coventry, United Kingdom 176 Waseda University, Tokyo, Japan 177 Department of Particle Physics, Weizmann Institute of Science, Rehovot, Israel 178 Department of Physics, University of Wisconsin, Madison, Wisconsin, USA 179 Fakultät für Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal, Germany 180 Department of Physics, Yale University, New Haven, Connecticut, USA 181 Yerevan Physics Institute, Yerevan, Armenia a Deceased. b Also at Department of Physics, King’s College London, London, United Kingdom. c Also at Istanbul University, Dept. of Physics, Istanbul, Turkey. d Also at Instituto de Física Teórica de la Universidad Autónoma de Madrid, Spain. e Also at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan. f Also at TRIUMF, Vancouver, British Columbia, Canada. g Also at Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky, USA. h Also at Department of Physics, University of Fribourg, Fribourg, Switzerland. i Also at Physics Dept, University of South Africa, Pretoria, South Africa. j Also at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona, Spain. k Also at Tomsk State University, Tomsk, and Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia. l Also at The Collaborative Innovation Center of Quantum Matter (CICQM), Beijing, China. m Also at Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal. n Also at Universita di Napoli Parthenope, Napoli, Italy. o Also at Institute of Particle Physics (IPP), Canada. p Also at II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany. q Also at Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania. r Also at CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France. s Also at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg, Russia. t Also at Borough of Manhattan Community College, City University of New York,, New York, USA. 072009-37 M. AABOUD et al. PHYS. REV. D 99, 072009 (2019) u Also at Department of Physics, California State University, Fresno, California, USA. v Also at Department of Financial and Management Engineering, University of the Aegean, Chios, Greece. w Also at Centre for High Performance Computing, CSIR Campus, Rosebank, Cape Town, South Africa. x Also at Louisiana Tech University, Ruston, Los Angeles, USA. y Also at California State University, East Bay, USA. z Also at Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona, Spain. aa Also at Department of Physics, University of Michigan, Ann Arbor, Michigan, USA. bb Also at LAL, Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France. cc Also at Graduate School of Science, Osaka University, Osaka, Japan. dd Also at Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany. ee Also at Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands. ff Also at Institute of Theoretical Physics, Ilia State University, Tbilisi, Georgia. gg Also at CERN, Geneva, Switzerland. hh Also at Department of Physics, Stanford University, USA. ii Also at Manhattan College, New York, New York, USA. jj Also at Joint Institute for Nuclear Research, Dubna, Russia. kk Also at Hellenic Open University, Patras, Greece. ll Also at LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3, Paris, France. mm Also at The City College of New York, New York, New York, USA. nn Also at Departamento de Física Teorica y del Cosmos, Universidad de Granada, Granada (Spain), Spain. oo Also at Department of Physics, California State University, Sacramento, California, USA. pp Also at Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia. qq Also at Département de Physique Nucléaire et Corpusculaire, Université de Genève, Genève, Switzerland. rr Also at Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom. ss Also at School of Physics, Sun Yat-sen University, Guangzhou, China. tt Also at Department of Applied Physics and Astronomy, University of Sharjah, Sharjah, United Arab Emirates. uu Also at Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany. vv Also at National Research Nuclear University MEPhI, Moscow, Russia. ww Also at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary. xx Also at Giresun University, Faculty of Engineering, Giresun, Turkey. yy Also at Institute of Physics, Academia Sinica, Taipei, Taiwan. 072009-38