Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at √s = 8TeV
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AuthorKhachatryan, Vladimir; Brochero Cifuentes, Javier Andrés; Cabrillo Bartolomé, José Iban; Calderón Tazón, Alicia; Duarte Campderros, Jorge; Fernández García, Marcos; Gómez Gramuglio, Gervasio; Graziano, Alberto; López Virto, María Amparo; Marco de Lucas, Jesús; Marco de Lucas, Rafael José; Martínez Rivero, Celso; Matorras Weinig, Francisco; Muñoz Sánchez, Francisca Javiela; Piedra Gómez, Jonatan; Rodrigo Anoro, Teresa; Rodríguez Marrero, Ana Yaiza; Ruiz Jimeno, Alberto; Scodellaro, Luca; [et al.]
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 vs = 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¯Wtt¯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 stt¯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, stt¯Z=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 tt¯V process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.