Measurements of the Production Cross Section of a Z Boson in Association with Jets in pp Collisions at √s̅ = 13 TeV with the ATLAS Detector

A measurement of the tt̅ Z and tt̅ 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 √s̅ = 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 σ_{tt̅ Z} = 0.9 ± 0.3 pb and σ_{tt̅ W} = 1.5 ± 0.8 pb, in agreement with the Standard Model predictions.