This paper describes a measurement of the inclusive top quark pair production cross-section (σtt̄) with a data sample of 3.2 fb−1 of proton-proton collisions at a centre-of-mass energy of √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 σtt̄and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be: σtt̄ = 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.

Aaboud, M., Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Abeloos, B., et al. (2016). Measurement of the tt¯ production cross-section using eμ events with b-tagged jets in pp collisions at √s = 13 TeV with the ATLAS detector. PHYSICS LETTERS. SECTION B, 761, 136-157 [10.1016/j.physletb.2016.08.019].

Measurement of the tt¯ production cross-section using eμ events with b-tagged jets in pp collisions at √s = 13 TeV with the ATLAS detector

F. Ceradini;B. Di Micco;R. Di Nardo;D. Orestano;F. Petrucci;D. Puddu;