Measurement of the tt¯ production cross-section using e[mu] events with b-tagged jets in pp collisions at [square root]s=13TeV with the ATLAS detector

Abstract

This paper describes a measurement of the inclusive top quark pair production cross-section ([sigma]tt¯) with a data sample of 3.2 fb−1 of proton–proton collisions at a centre-of-mass energy of [square root]s = 13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron–muon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously [sigma]tt¯and the efficiency to reconstruct and btag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be: [sigma]tt¯= 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented.