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Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at √s = 8 TeV

A measurement of the cross section for the production of top quark–antiquark pairs (tt) in association with a vector boson V (W or Z) in proton-proton collisions at √s = 8 TeV is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 fb−1 recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and µ) channels: a samesign dilepton analysis targeting ttW events, and trilepton and four-lepton analyses designed for ttZ events. In the samesign dilepton channel, the ttW cross section is measured as σttW = 170+90 −80 (stat) ± 70 (syst) fb, corresponding to a significance of 1.6 standard deviations over the backgroundonly hypothesis. Combining the trilepton and four- lepton channels, a direct measurement of the ttZ cross section, σttZ = 200+80 −70 (stat)+40 −30 (syst)fb−1, is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive ttV process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.

CMS; pp; 8 TeV. Top Quark

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