Measurement of the t[bar over t]W and t[bar over t]Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector

Abstract

The production cross sections of top-quark pairs in association with massive vector bosons have been measured using data from pp collisions at √s = 8 TeV. The dataset corresponds to an integrated luminosity of 20.3 fb[superscript −1] collected by the ATLAS detector in 2012 at the LHC. Final states with two, three or four leptons are considered. A fit to the data considering the t[bar over t]W and t[bar over t]Z processes simultaneously yields a significance of 5.0σ (4.2σ) over the background-only hypothesis for t[bar over t]W (t[bar over t]Z ) production. The measured cross sections are σ[subscript t[bar over t]W] = 369[superscript +100][subscript −91] fb and σ[subscript t[bar over t]Z]=176[superscript +58][subscript −52] fb. The background-only hypothesis with neither t[bar over t]W nor t[bar over t]Z production is excluded at 7.1σ. All measurements are consistent with next-to-leading-order calculations for the t[bar over t]W and t[bar over t]Z processes.