Measurement of the $t\bar{t}$ production cross-section in the lepton+jets channel at $\sqrt{s}=13$ TeV with the ATLAS experiment

The $t\bar{t}$ production cross-section is measured in the lepton+jets channel using proton-proton collision data at a center-of-mass-energy of $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC. The data set corresponds to an integrated luminosity of ${\mathcal L}=139$ fb$^{-1}$. Events with exactly one charged lepton, at least four jets and at least one $b$-tagged jet in the final state are used to determine the $t\bar{t}$ production cross-section through a profile-likelihood fit. The fiducial $t\bar{t}$ cross-section within the experimental acceptance is measured to be ${\sigma_{\text{fid}} = 110.78 \pm 0.05 \text{ (stat.) }_{-4.38}^{+4.59} \text{ (syst.)}~\mathrm{pb}}$, corresponding to a relative uncertainty of 4.1%. The inclusive cross-section is ${\sigma_{\text{inc}} = 830.4 \pm 0.4 \text{ (stat.) }_{-37.0}^{+38.2} \text{ (syst.)}~\mathrm{pb}} $ with a relative uncertainty of 4.6%. The result is consistent with the theoretical calculations at next-to-next-to-leading order in QCD perturbation theory.