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 ttW events, and trilepton and four-lepton analyses designed for ttZ events. In the same-sign dilepton channel, the ttW cross section is measured as σ(ttW) = 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 ttZ cross section, σ(ttZ) = 200+80−70 (stat)+40−30 (syst) fb, 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.
Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at √s = 8 TeV
Sola V;AMAPANE, Nicola Carlo;BELLAN, Riccardo;CASASSO, STEFANO;COSTA, Marco;DEGANO, Alessandro;FINCO, LINDA;MIGLIORE, Ernesto;MONACO, Vincenzo;MUSICH, MARCO;OBERTINO, Maria Margherita;ORTONA, GIACOMO;PACHER, LUCA;PINNA ANGIONI, GIAN LUCA;POTENZA, ALBERTO;ROMERO, Alessandra;SACCHI, Roberto;SOLANO, Ada Maria;TAMPONI, UMBERTO;COVARELLI, Roberto;
2014-01-01
Abstract
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 ttW events, and trilepton and four-lepton analyses designed for ttZ events. In the same-sign dilepton channel, the ttW cross section is measured as σ(ttW) = 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 ttZ cross section, σ(ttZ) = 200+80−70 (stat)+40−30 (syst) fb, 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.
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