Measurement of the $t\bar{t}Z$ cross section in the four lepton channel at 13 TeV with ATLAS

The measurement of a Z boson together with a top quark pair in the four lepton channel is presented. The analysis uses the first 3.2 fb$^{-1}$ data at $\sqrt{s}=$13 Te\kern -0.1em V which were recorded by the ATLAS detector at the Large Hadron Collider in 2015. The inclusive t\={t}Z cross section is extracted using a likelihood fit to signal and control regions in the three and four lepton channel, resulting in $\sigma _{\textit{t\={t}Z}} = 0.92 \pm 0.30 \mathrm{(stat.)} \pm 0.11 \mathrm{(syst.) pb}.$