Measurement of the tt⎯⎯W T T ¯ W and tt⎯⎯Z T T ¯ Z Production Cross Sections in Pp Collisions at S√=8 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 ��√=8 TeV. The dataset corresponds to an integrated luminosity of 20.3 fb−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 ����⎯⎯�� and ����⎯⎯�� processes simultaneously yields a significance of 5.0σ (4.2σ) over the background-only hypothesis for ����⎯⎯�� (����⎯⎯��) production. The measured cross sections are ������⎯⎯��=369+100−91 fb and ������⎯⎯��=176+58−52 fb. The background-only hypothesis with neither ����⎯⎯�� nor ����⎯⎯�� production is excluded at 7.1σ. All measurements are consistent with next-to-leading-order calculations for the ����⎯⎯�� and ����⎯⎯�� processes.