Abstract
A measurement of the associated production of a top-quark pair ($t\bar{t}$) 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 $t\bar{t}Z$ and $t\bar{t}W$ production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are $\sigma_{t\bar{t}Z} = 0.95 \pm 0.08_{\mathrm{stat.}} \pm 0.10_{\mathrm{syst.}}$ pb and $\sigma_{t\bar{t}W} = 0.87 \pm 0.13_{\mathrm{stat.}} \pm 0.14_{\mathrm{syst.}}$ pb in agreement with the Standard Model predictions. The measurement of the $t\bar{t}Z$ cross section is used to set constraints on effective field theory operators which modify the $t\bar{t}Z$ vertex.
Highlights
Properties of the top quark have been explored by the Large Hadron Collider (LHC) and previous collider experiments in great detail
This paper presents measurements of the ttZ and ttW ccreonstsers-eocftimonasssuesninegrgpyroptoffisffin1⁄4-pr1o3toTne(Vppc)orcroelslpisoionndindgatatoatana integrated luminosity of 36.1 fb−1, collected by the ATLAS detector in 2015 and 2016
Electron candidates [58] are reconstructed from energy deposits in the EM calorimeter that are associated with reconstructed tracks in the inner detector (ID)
Summary
Properties of the top quark have been explored by the Large Hadron Collider (LHC) and previous collider experiments in great detail. Measurements of top-quark pairs in association with a Z or W boson (ttZ and ttW) provide a direct probe of the weak couplings of the top quark [9,10,11] These couplings may be modified in the presence of physics beyond the Standard Model (BSM). If no deviations are observed, measurements of the ttZ and ttW production cross sections, σttZ and σttW, can be used to set constraints on the weak couplings of the top quark in the. The production of ttZ and ttW is often an important background in searches involving final states with multiple leptons and b-quarks These processes constitute an important background in measurements of the associated production of the Higgs boson with top quarks. The final states of top-quark pairs produced in association with a Z or a W boson contain up to four isolated, prompt leptons.. An interpretation of the ttZ cross-section measurement in the SMEFT framework is performed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
