Measurement of the $t\bar{t}Z$ and $t\bar{t}W$ production cross sections in multilepton final states using 3.2 fb$^{-1}$ of $pp$ collisions at 13 TeV at the LHC

A measurement of the $t\bar{t}Z$ and $t\bar{t}W$ 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 $\sqrt{s} = 13$ Te\kern -0.1em V recorded with the ATLAS detector at the Large Hadron Collider in 2015 corresponding to a total integrated luminosity of \mbox{3.2 fb$^{-1}$}. The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in $\sigma_{t\bar{t}Z} = 0.9 \pm 0.3$ pb and $\sigma_{t\bar{t}W} = 1.4 \pm 0.8$ pb, in agreement with the Standard Model predictions.