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

TL;DR

This paper reports a precise measurement of the production rate and kinematic properties of top-antitop quark pairs produced with a Z boson at 13 TeV, using the full ATLAS Run 2 dataset.

Contribution

It provides the first comprehensive measurement of inclusive and differential cross sections of t-tbar-Z production at 13 TeV with detailed kinematic analysis.

Findings

Measured cross section of 1.05 pb with uncertainties in agreement with Standard Model.

Performed differential measurements to explore kinematic distributions.

Validated theoretical predictions with experimental data.

Abstract

The inclusive as well as differential cross section of the associated production of top-antitop quark pairs and a $Z$ boson ($t\bar{t}Z$) is measured in final states with exactly three or four isolated leptons (electrons or muons). For this purpose, the full LHC Run 2 dataset of proton-proton collisions recorded by the ATLAS detector from $2015$ to $2018$, which corresponds to an integrated luminosity of $139\,\text{fb}^{-1}$, is used. The inclusive production cross section is measured to be $\sigma_{t\bar{t}Z}=1.05\pm0.05\,(\text{stat.})\,\pm0.09\,(\text{syst.})\,\text{pb}$, which is in agreement with the most precise Standard Model theoretical prediction. Absolute and normalised differential cross section measurements are performed as a function of various kinematic variables in order to probe the kinematics of the $t\bar{t}Z$ system within both parton- and particle-level phase spaces.