Abstract
Abstract:
The inclusive and fiducial tt¯ 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 tt¯
cross-section is measured with a precision of 5.7% to be σinc(tt¯) = 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 σfid(tt¯) =
48.8 ± 0.1 (stat.) ± 2.0 (syst.) ± 0.9 (lumi.) pb with a precision of 4.5%.