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 same-sign dilepton analysis targeting tt‾W events, and trilepton and four-lepton analyses designed for tt‾Z events. In the same-sign dilepton channel, the tt‾W cross section is measured as σtt‾W = 170+90−80 (stat) ± 70 (syst) fb, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the tt‾Z cross section, σtt‾Z = 200+80−70 (stat)+40−30 (syst)fb−1, is obtained with a significanceof 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive tt‾V process is observed with a significance of 3.7 standard deviations fromthe combination of all three leptonic channels.
- Squark pair