Abstract
A measurement is performed of the cross section of top quark pair production in association with a W or Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb−1, collected by the CMS experiment in 2016. The measurement is performed in the same-sign dilepton, three- and four-lepton final states. The production cross sections are measured to be sigma left(mathrm{t}overline{mathrm{t}}mathrm{W}right)={0.77}_{-0.11}^{+0.12}{left(mathrm{stat}right)}_{-0.12}^{+0.13}left(mathrm{syst}right)mathrm{p}mathrm{b} and sigma left(mathrm{t}overline{mathrm{t}}mathrm{Z}right)={0.99}_{-0.08}^{+0.09}{left(mathrm{stat}right)}_{-0.10}^{+0.12}left(mathrm{syst}right)mathrm{p}mathrm{b} . The expected (observed) signal significance for the mathrm{t}overline{mathrm{t}}mathrm{W} production in same-sign dilepton channel is found to be 4.5 (5.3) standard deviations, while for the mathrm{t}overline{mathrm{t}}mathrm{Z} production in three- and four-lepton channels both the expected and the observed significances are found to be in excess of 5 standard deviations. The results are in agreement with the standard model predictions and are used to constrain the Wilson coefficients for eight dimension-six operators describing new interactions that would modify mathrm{t}overline{mathrm{t}}mathrm{W} and mathrm{t}overline{mathrm{t}}mathrm{Z} production.
Highlights
Background predictions5.1 Background due to nonprompt leptonsNonprompt leptons, i.e. leptons from heavy-flavor hadron decay, misidentified hadrons, muons from light meson decays, or electrons from unidentified photon conversions, are strongly rejected by the identification and the isolation criteria applied on electrons and muons
A measurement is performed of the cross section of top quark pair production in association with a W or Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC
Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections
Summary
The measurements are performed using events in which at least one of the W bosons, originating from a top quark decay, further decays to a charged lepton and a neutrino, and the associated W or Z boson decays to a charged lepton and a neutrino or a charged lepton pair, where the charged lepton ( ) refers to an electron or a muon. The analysis is performed in three exclusive final states, in which events with two leptons of same charge, denoted as same-sign (SS) dileptons, are used to extract the ttW signal, while events with three or four charged leptons that include a lepton pair of opposite charge and same flavor (OSSF) are used to measure the ttZ signal yield. In addition to the individual ttW and ttZ cross section measurements, a fit is performed in all three final states to simultaneously extract these cross sections. The results are interpreted in the context of an effective field theory to constrain the Wilson coefficients [9], which parameterize the strength of new physics interactions, for a set of selected dimension-six operators that might signal the presence of NP contributions in ttW and ttZ production
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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
