Search for leptonic charge asymmetry in tt¯W production in final states with three leptons at s√=13 TeV

A search for the leptonic charge asymmetry (Aℓc) of top-quark−antiquark pair production in association with a W boson (tt¯W) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on s√=13 TeV proton−proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN during the years 2015−2018, corresponding to an integrated luminosity of 139 fb−1. A profile-likelihood fit to the event yields in multiple regions corresponding to positive and negative differences between the pseudorapidities of the charged leptons from top-quark and top-antiquark decays is used to extract the charge asymmetry. At reconstruction level, the asymmetry is found to be −0.123±0.136 (stat.) ±0.051 (syst.). An unfolding procedure is applied to convert the result at reconstruction level into a charge-asymmetry value in a fiducial volume at particle level with the result of −0.112±0.170 (stat.) ±0.054 (syst.). The Standard Model expectations for these two observables are calculated using Monte Carlo simulations with next-to-leading-order plus parton shower precision in quantum chromodynamics and including next-to-leading-order electroweak corrections. They are −0.084+0.005−0.003 (scale) ±0.006 (MC stat.) and −0.063+0.007−0.004 (scale) ±0.004 (MC stat.) respectively, and in agreement with the measurements.