Addendum to ‘Measurement of the t\bar{t} t t ¯ production cross-section using e\mu e μ events with b-tagged jets in pp collisions at \sqrt{s} s = 7 and 8 \,\mathrm{TeV} TeV with the ATLAS detector’

English (OpenAlex)

The ATLAS measurement of the inclusive top quark pair (t t) cross-section σ t t in proton-proton collisions at √ s = 8 TeV has been updated using the final 2012 luminosity calibration.The updated cross-section result is: σ t t = 242.9± 1.7 ± 5.5 ± 5.1 ± 4.2 pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, knowledge of the integrated luminosity and of the LHC beam energy.The result is consistent with theoretical QCD calculations at nextto-next-to-leading order.The measurement of the ratio of t t cross-sections at √ s = 8 TeV and √ s = 7 TeV, and the √ s = 8 TeV fiducial measurement corresponding to the experimental acceptance of the leptons, have also been updated.The most precise measurement of the t t cross-section (σ t t ) in proton-proton collisions at √ s = 8 TeV from the ATLAS Collaboration was made using events with an oppositecharge electron-muon pair and one or two b-tagged jets [1], and used a preliminary calibration of the integrated luminosity.The luminosity calibration has been finalised since [2] with a total uncertainty of 1.9%, corresponding to a substantial improvement on the previous uncertainty of 2.8%.Since the uncertainty on the integrated luminosity contributed 3.1% of the total 4.3% uncertainty on the σ t t measurement reported in [1], a significant improvement in the measurement is possible by using the new luminosity calibration, as documented in this Addendum.The new calibration corresponds to an integrated luminosity of 20.2 fb -1 for the √ s = 8 TeV sample, a decrease of 0.2%.The cross-section was recomputed taking into account the effects on both the conversion of the t t event yield to a cross-section, and the background estimates, giving a result of: σ t t = 242.9± 1.7 ± 5.5 ± 5.1 ± 4.2 pb,