# Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at $\sqrt{s} = 8$ $\,\text {TeV}$

The European Physical Journal C, Sep 2014

A measurement of the cross section for the production of top quark–antiquark pairs ( ${\mathrm {t}}\overline{{\mathrm {t}}}$ ) in association with a vector boson V (W or Z) in proton-proton collisions at $\sqrt{s} = 8$ $\,\text {TeV}$ 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 $\upmu$ ) channels: a same-sign dilepton analysis targeting ${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}$ events, and trilepton and four-lepton analyses designed for ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}$ events. In the same-sign dilepton channel, the ${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}$ cross section is measured as $\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}} = 170 ^{+90}_{-80}\,\text {(stat)} \pm 70\,\text {(syst)} \, \text {fb}$ , 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 ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}$ cross section, $\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}} = 200 ^{+80}_{-70}\,\text {(stat)} ^{+40}_{-30}\,\text {(syst)} \mathrm{fb}^{-1}$ , 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 ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {V}}$ process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.

This is a preview of a remote PDF: http://link.springer.com/content/pdf/10.1140%2Fepjc%2Fs10052-014-3060-7.pdf

V. Khachatryan, A. M. Sirunyan, A. Tumasyan, W. Adam, T. Bergauer, M. Dragicevic, J. Erö, C. Fabjan, M. Friedl, R. Frühwirth, V. M. Ghete, C. Hartl, N. Hörmann, J. Hrubec, M. Jeitler, et al. Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at $\sqrt{s} = 8$ $\,\text {TeV}$, The European Physical Journal C, 2014, DOI: 10.1140/epjc/s10052-014-3060-7