Measurement of the top-quark pole mass in dileptonic $$ t\overline{t} $$ + 1-jet events at $$ \sqrt{s}=13 $$ TeV with the ATLAS experiment

A bstract A measurement of the top-quark pole mass $$ {m}_t^{\textrm{pole}} $$ m t pole is presented in $$ t\overline{t} $$ t t ¯ events with an additional jet, $$ t\overline{t} $$ t t ¯ + 1-jet, produced in pp collisions at $$ \sqrt{s}=13 $$ 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 $$ t\overline{t} $$ t t ¯ + 1-jet differential cross-section as a function of the inverse of the invariant mass of the $$ t\overline{t} $$ t t ¯ + 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 $$ pp\to t\overline{t}j\left(2\to 3\right) $$ pp → t t ¯ j 2 → 3 , where top quarks are taken as stable particles, and the process $$ pp\to b\overline{b}{l}^{+}\nu {l}^{-}\overline{\nu}j\left(2\to 7\right) $$ pp → b b ¯ l + ν l − ν ¯ j 2 → 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 χ 2 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: $$ {m}_t^{\textrm{pole}}=170.7\pm 0.3\left(\textrm{stat}.\right)\pm 1.4\left(\textrm{syst}.\right)\pm 0.3\left(\textrm{scale}\right)\pm 0.2\left(\textrm{PDF}\oplus {\alpha}_{\textrm{S}}\right) $$ m t pole = 170.7 ± 0.3 stat . ± 1.4 syst . ± 0.3 scale ± 0.2 PDF

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