Top-quark pair production in association with a Z boson in the final state with four charged leptons

The production cross section of a top-quark pair in association with a Z boson is measured in the channel with four reconstructed leptons, using 36.1 fb${}^{-1}$ of proton-proton collisions, collected with the ATLAS detector at the Large Hadron Collider at CERN. A profile likelihood fit is performed, using four signal regions and a control region for the ZZ background. A total of 48 events are observed in the signal regions and a t$\overline{t}$Z cross section of σ${}_{t\overline{t}Z}$ = 1.07${}_{-0.25}^{+0.28}$ (stat.)${}_{-0.09}^{+0.10}$ (syst.)pb is extracted, which is compatible with the Standard Model calculation. Combined with other channels, the measured cross section is σ${}_{t\overline{t}Z}$ = 0.95 ± 0.08 , (stat.) ± 0.10 (syst.)pb. Data is unfolded in the 4$\ell$ channel, to compute the differential cross section for p${}_T$(Z($\ell \ell$)) and ΔΦ${}_{Z\left(\ell \ell \right)}$, variables sensitive to EFT operators, that modify the $t\overline{t}$Z vertex.