# Top-quark pair production in association with a $Z$ boson in the 4$\ell$ channel with the ATLAS experiment

## TL;DR

This paper reports a measurement of the top-quark pair production in association with a Z boson in the four-lepton channel using ATLAS data, confirming consistency with Standard Model predictions.

## Contribution

First measurement of the $t\bar{t}Z$ cross section in the 4-lepton channel with ATLAS at 13 TeV, providing a precise test of the Standard Model.

## Key findings

- Measured $t\bar{t}Z$ cross section: 1.07 ± 0.26 pb
- Results are consistent with Standard Model predictions
- Performed simultaneous fit for $t\bar{t}Z$ and $t\bar{t}W$ processes

## Abstract

The cross section of the $t\bar{t}Z$~and $t\bar{t}W$~processes are measured in a simultaneous fit using 36.1 $\text{fb}^{-1}$ of of proton--proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded by the ATLAS experiment at the LHC. In addition, a fit is performed in the 4$\ell$ channel only, resulting in a cross section of $\sigma_{t\bar{t}Z} = 1.07 \pm 0.26 \,\text{pb}$. This result is consistent with the combined fit and agrees with the prediction by the Standard Model.