Measurement of the Production Cross-section in the Lepton+jets Channel at TeV with the ATLAS experiment

The top anti-top quark production cross-section is measured in the lepton+jets channel using proton–proton collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb$^{−1}$. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing b-hadrons, are used to determine the $t\overline{t}$ production cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be ${\sigma }_{\text{inc}}=830±0.4\phantom{\rule{0.25em}{0ex}}\text{(stat.)}±36\phantom{\rule{0.25em}{0ex}}\text{(syst.)}±14\phantom{\rule{0.25em}{0ex}}\text{(lumi.)}\phantom{\rule{0.25em}{0ex}}\mathrm{pb}$ with a relative uncertainty of 4.6%. The result is consistent with theoretical calculations at next-to-next-to-leading order in perturbative QCD. The fiducial $t\overline{t}$ cross-section within the experimental acceptance is also measured.