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−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 tt¯W and tt¯Z processes simultaneously yields a significance of 5.0σ (4.2σ) over the background-only hypothesis for tt¯W (tt¯Z) production. The measured cross sections are (Formula presented.) fb and (Formula presented.) fb. The background-only hypothesis with neither tt¯W nor tt¯Z production is excluded at 7.1σ. All measurements are consistent with next-to-leading-order calculations for the tt¯W and tt¯Z processes.[Figure not available: see fulltext.]
Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., et al. (2015). Measurement of the tt¯W and tt¯Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector. JOURNAL OF HIGH ENERGY PHYSICS, 2015(11), 1-48 [10.1007/JHEP11(2015)172].