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 ?(tt¯W)=0.77?0.11+0.12(stat)?0.12+0.13(syst)pb and ?(tt¯Z)=0.99?0.08+0.09(stat)?0.10+0.12(syst)pb. The expected (observed) signal significance for the t t ¯ W production in same-sign dilepton channel is found to be 4.5 (5.3) standard deviations, while for the t 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 t ¯ W and t t ¯ Z production.

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