Measurement of the top-quark pole mass in dileptonic ttbar + 1-jet events at sqrt(s) = 13 TeV with the ATLAS experiment

A measurement of the top-quark pole mass mtpole is presented in tt¯ events with an additional jet, ttbar + 1-jet, produced in pp collisions at sqrt(s) = 13 TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of 140 fb-1. Events with one electron and one muon of opposite electric charge in the final state are selected to measure the ttbar + 1-jet differential cross-section as a function of the inverse of the invariant mass of the ttbar + 1-jet system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process pp -> ttbar j2 -> 3, where top quarks are taken as stable particles, and the process pp -> bbbarl + nul-νmarj2 -> 7, which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using a chi2 fit of the unfolded normalized differential cross-section distribution. The results obtained with the 2 -> 3 and 2 -> 7 calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the 2 -> 3 measurement: mtpole = 170.7 +- 0.3stat. +- 1.4syst. +- 0.3scale +- 0.2PDF + alphaS GeV, which is in good agreement with other top-quark mass results.