Search for leptonic charge asymmetry in $$ t\overline{t}W $$ production in final states with three leptons at $$ \sqrt{s} $$ = 13 TeV

Abstract A search for the leptonic charge asymmetry ( $$ {A}_{\textrm{c}}^{\ell } $$ A c ℓ ) of top-quark-antiquark pair production in association with a W boson ( $$ t\overline{t}W $$ t t ¯ W ) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on $$ \sqrt{s} $$ 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 −0.12 ± 0.14 (stat.) ± 0.05 (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 −0.11 ± 0.17 (stat.) ± 0.05 (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 $$ -{0.084}_{-0.003}^{+0.005} $$ − 0.084 − 0.003 + 0.005 (scale) ± 0.006 (MC stat.) and $$ -{0.063}_{-0.004}^{+0.007} $$ − 0.063 − 0.004 + 0.007 (scale) ± 0.004 (MC stat.) respectively, and in agreement with the measurements.

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