Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment

TL;DR

This paper reports a measurement of the charge asymmetry in top-quark pair production with an associated photon, using ATLAS data at 13 TeV, finding results consistent with the Standard Model.

Contribution

First measurement of charge asymmetry in top-quark pairs produced with a photon at the LHC using ATLAS data.

Findings

Charge asymmetry measured as A_C = -0.003 ± 0.029

Results are consistent with Standard Model predictions

Utilized profile likelihood unfolding approach

Abstract

A measurement of the charge asymmetry in top-quark pair ($t\bar{t}$) production in association with a photon is presented. The measurement is performed in the single-lepton $t\bar{t}$ decay channel using proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015-2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be $A_\text{C}=-0.003 \pm 0.029$ in agreement with the Standard Model expectation.