Measurement of the tt¯W and tt¯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 bosonshave been measured using data from pp collisions at √s = 8 TeV. The dataset correspondsto an integrated luminosity of 20.3 fb−1collected by the ATLAS detector in 2012at the LHC. Final states with two, three or four leptons are considered. A fit to the dataconsidering the ttW¯ and ttZ¯ processes simultaneously yields a significance of 5.0σ (4.2σ)over the background-only hypothesis for ttW¯ (ttZ¯ ) production. The measured cross sectionsare σttW¯ = 369+100−91 fb and σttZ¯ = 176+58−52 fb. The background-only hypothesis with neitherttW¯ nor ttZ¯ production is excluded at 7.1σ. All measurements are consistent with next-toleading-ordercalculations for the ttW¯ and ttZ¯ processes.