Measurement of the inclusive and differential cross section of a top quark pair in association with a $Z$ boson at $13\,\text{TeV}$ with the ATLAS detector

In the Standard Model of Particle Physics, the coupling of the $Z$ boson to top quarks is precisely predicted via the weak interaction. As its value is experimentally not yet well constrained, several possible extensions of the Standard Model predicting modifications to this coupling could not be ruled out nor confirmed so far. Therefore a more accurate understanding of electroweak processes could significantly benefit from a precise measurement of this coupling at the LHC. In this analysis, the $t\bar{t}Z$ process is studied in final states featuring 3 and 4 charged leptons, using the full Run2 dataset taken in the years 2015 to 2018 which corresponds to an integrated luminosity of $139\,\text{fb}^{-1}$. In order to extract the inclusive production cross section, a combined profile-likelihood fit is performed. The $WZ$/$ZZ$+jets backgrounds are estimated in dedicated control regions, whereas for the fake lepton background a data-driven approach is used. For the differential measurements of the absolute and normalised cross sections, 9 variables sensitive to the kinematics of the $t\bar{t}Z$ system are unfolded to both parton- as well as particle level and compared to the predictions of several Monte Carlo generators.