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

Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hartl, C. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Krätschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Wulz, C.-E. and Filipovic, Nicolas and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Béni, Noémi Tekla and Karancsi, János and Molnár, József and Pálinkás, József and Szillási, Zoltán and Raics, Péter and Trócsányi, Zoltán and Ujvári, Balázs and Veres, Gábor (2014) Measurement of top quark-antiquark pair production in association with a W or Z boson in pp collisions at√s = 8 TeV. EUROPEAN PHYSICAL JOURNAL C, 74 (9). ISSN 1434-6044

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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 de- signed for ttZ events. In the same-sign 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 background-only 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, is obtained with a significance of 3.1 standard devi- ations. 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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