Abstract
This paper describes a measurement of the inclusive top quark pair production cross-section (σtt¯) 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 σtt¯ and 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: σtt¯ = 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.
Highlights
The top quark is the heaviest known fundamental particle, with a mass mt which is much larger than any of the other quarks, and close to the scale of electroweak symmetry breaking
13 TeV pp collisions recorded by the ATLAS detector at the LHC
Assuming a top quark mass of mt = 172.5 GeV, the result is: σtt = 818 ± 8 ± 27 ± 19 ± 12 pb, where the four uncertainties are due to data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%
Summary
The top quark is the heaviest known fundamental particle, with a mass mt which is much larger than any of the other quarks, and close to the scale of electroweak symmetry breaking. Calculations of the ttproduction cross-section at hadron colliders are available at full next-to-next-to-leading-order (NNLO) accuracy in the strong coupling constant αS, including the resummation of next-to-next-to-leading logarithmic (NNLL) soft gluon terms [1,2,3,4,5]. In this pape√r a reference value of 832+−4406 pb at a centre-of-mass energy of s = 13 TeV assuming mt = 172.5 GeV is used, corresponding to a relative precision of +−45..85%. Powheg-Box v2 + Pythia Powheg-Box v2 + Herwig++ Madgraph5_aMC@NLO + Herwig++ Powheg-Box v1 + Pythia Powheg-Box v1 + Herwig++ Sherpa 2.1.1 Sherpa 2.1.1 Powheg + Pythia Powheg-Box v1 + Pythia Powheg-Box v2 + Pythia MadGraph + Pythia
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