Measurement of the inclusive and fiducial tt̄ production cross-sections in the lepton+jets channel in pp collisions at √s = 8 TeV with the ATLAS detector

The inclusive and fiducial tt̄ production cross-sections are measured in the lepton+jets channel using 20.2 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 + jets process is modelled using Z+ jets events in a data-driven approach. The inclusive tt̄ cross-section is measured with a precision of 5.7% to be σ_inc(tt̄) = 248.3 ± 0.7 (stat.) ±13.4 (syst.) ±4.7 (lumi.) 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 σ_fid(tt̄) = 48.8 ± 0.1 (stat.) ±2.0 (syst.) ±0.9 (lumi.) pb with a precision of 4.5%.