Measurement of the cross-section for the associated production of a top quark pair and a W or Z boson with the ATLAS detector

In the Standard Model the coupling of the top quark to a vector boson is predicted via the weak interaction. New physics beyond the Standard Model can modify the $t\bar{t}V$ cross-section. As an example several of the operators introduced by effective field theory are sensitive to the $t\bar{t}Z$ and $t\bar{t}W$ production cross-sections. Multiple analysis channels with 2, 3 or 4 lepton final-states have been considered in the latest $t\bar{t}V$ cross section measurement by the ATLAS experiment. The dominant backgrounds in the analysis are mis-reconstructed leptons and the diboson process, depending on the analysis channel. A two-dimensional fit of the $t\bar{t}W$ and $t\bar{t}Z$ cross-section is performed to interpret possible deviations from the Standard Model.