Measurement of the inclusive and fiducial $t\overline{t}$ production cross-sections in the lepton+jets channel in pp collisions at $\sqrt{s}=8\phantom{\rule{3.33333pt}{0ex}}\text{TeV}$ with the ATLAS detector

The inclusive and fiducial $t\overline{t}$ production cross-sections are measured in the lepton+jets channel using $20.2\phantom{\rule{3.33333pt}{0ex}}{\text{fb}}^{-1}$ of proton–proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and b-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the $W\text{+\,jets}$ process is modelled using $Z$ + jets events in a data-driven approach. The inclusive $t\overline{t}$ cross-section is measured with a precision of 5.7% to be ${\sigma }_{\text{inc}}\left(t\overline{t}\right)=248.3±0.7\phantom{\rule{0.166667em}{0ex}}\left(\mathrm{stat}.\right)±13.4\phantom{\rule{0.166667em}{0ex}}\left(\mathrm{syst}.\right)±4.7\phantom{\rule{0.166667em}{0ex}}\left(\mathrm{lumi}.\right)\phantom{\rule{3.33333pt}{0ex}}\text{pb}$ , assuming a top-quark mass of 172.5 GeV. The result is in agreement with the Standard Model prediction. The cross-section is also measured in a phase space close to that of the selected data. The fiducial cross-section is ${\sigma }_{\text{fid}}\left(t\overline{t}\right)=48.8±0.1\phantom{\rule{0.166667em}{0ex}}\left(\mathrm{stat}.\right)±2.0\phantom{\rule{0.166667em}{0ex}}\left(\mathrm{syst}.\right)±0.9\phantom{\rule{0.166667em}{0ex}}\left(\mathrm{lumi}.\right)\phantom{\rule{3.33333pt}{0ex}}\text{pb}$ with a precision of 4.5%.