Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs ($t\bar{ t}$) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a $pp$ collision energy of $\sqrt{ s}=13$ TeV and correspond to an integrated luminosity of 140 fb$^{ -1}$. The measurements use events containing an oppositely charged $e\mu$ pair and $b$-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton $p_{ \text{ T}}$ distributions is obtained by reweighting the $t\bar{ t}$ sample so as to reproduce the top-quark $p_{ \text{ T}}$ distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be \[ \sigma_{ t\bar{ t}} = 829 \pm 1\;(\textrm{ stat}) \pm 13\;(\textrm{ syst}) \pm 8\;(\textrm{ lumi}) \pm 2\; (\textrm{ beam})\ \textrm{ pb}, \] where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
Categories: hep-ex