Measurement of the $t\bar{t}$ production cross-section in $pp$ collisions at $\sqrt{s}=5.02$ TeV with the ATLAS detector

The inclusive top-quark pair ($t\bar{t}$) production cross-section $\sigma_{t\bar{t}}$ is measured in proton-proton collisions at a centre-of-mass energy $\sqrt{s}=5.02$ TeV, using 257 pb$^{-1}$ of data collected in 2017 by the ATLAS experiment at the LHC. The $t\bar{t}$ cross-section is measured in both the dilepton and single-lepton final states of the $t\bar{t}$ system and then combined. The combination of both measurements yields $\sigma_{t\bar{t}}=67.5\pm 0.9$(stat.) $\pm 2.3$ (syst.) $\pm 1.1$ (lumi.) $\pm 0.2$ (beam) pb, where the four uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the LHC beam energy, giving a total uncertainty of 3.9%. The result is in agreement with theoretical quantum chromodynamic calculations at next-to-next-to-leading order in the strong coupling constant, including the resummation of next-to-next-to-leading logarithmic soft-gluon terms, and constrains the parton distribution functions of the proton at large Bjorken-$x$.