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 \(\sigma \left(t\overline{t}W\right)={0.77}_{-0.11}^{+0.12}{\left(\mathrm{stat}\right)}_{-0.12}^{+0.13}\left(\mathrm{syst}\right)pb\) and \(\sigma \left(t\overline{t}Z\right)={0.99}_{-0.08}^{+0.09}{\left(\mathrm{stat}\right)}_{-0.10}^{+0.12}\left(\mathrm{syst}\right)pb\). The expected (observed) signal significance for the \(t\overline{t}W\) production in same-sign dilepton channel is found to be 4.5 (5.3) standard deviations, while for the \(t\overline{t}Z\) 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 \(t\overline{t}W\) and \(t\overline{t}Z\) production.
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