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

A measurement of the top-quark pole mass $m_t^{\text{pole}}$ is presented in $t\bar{t}$ events with an additional jet, $t\bar{t}+1\text{-jet}$, 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 $140{\text{fb}}^{-1}$. Events with one electron and one muon of opposite electric charge in the final state are selected to measure the $t\bar{t}+1\text{-jet}$ differential cross-section as a function of the inverse of the invariant mass of the $t\bar{t}+1\text{-jet}$ 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 $pp\to t\bar{t}j$ ($2\to 3$), where top quarks are taken as stable particles, and the process $pp\to b\bar{b}{l}^{+}\nu l^{-}\bar{\nu }j$ ($2\to 7$), which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using a ${\chi }^2$ fit of the unfolded normalized differential cross-section distribution. The results obtained with the $2\to 3$ and $2\to 7$ calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the $2\to 3$ measurement: $m_t^{\text{pole}}=170.7\pm 0.3(\text{stat.})\pm 1.4(\text{syst.})\pm 0.3(\text{scale})\pm 0.2(\text{PDF}\oplus {\alpha }_{\text{S}})\text{ GeV},$ which is in good agreement with other top-quark mass results.