A measurement of the tt¯ Z and tt¯ W production cross sections in final states with either two same-charge muons, or three or four leptons (electrons or muons) is presented. The analysis uses a data sample of proton–proton collisions at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015, corresponding to a total integrated luminosity of 3.2 fb- 1. The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in σtt¯Z= 0.9 ± 0.3 pb and σtt¯W= 1.5 ± 0.8 pb, in agreement with the Standard Model predictions.
Aaboud, M., Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Abeloos, B., et al. (2017). Measurement of the tt¯Z and tt¯W production cross sections in multilepton final states using 3.2 fb -1 of pp collisions at √s = 13 TeV with the ATLAS detector. THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS, 77(1), 40 [10.1140/epjc/s10052-016-4574-y].