Measurement of the t ¯t Z and t ¯tW production cross sections inmultilepton final states using 3.2 fb−1 of pp collisions at√s = 13TeV with the ATLAS detector

A measurement of the tt ¯ Z tt¯Z and tt ¯ W 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 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 −1 . The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in σ tt ¯ Z =0.9±0.3 σtt¯Z=0.9±0.3 pb and σ tt ¯ W =1.5±0.8 σtt¯W=1.5±0.8 pb, in agreement with the Standard Model predictions.