Abstract

This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair left(mathrm{t}overline{mathrm{t}}right) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The data correspond to integrated luminosities of about 5 and 20 fb−1 for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are ACCHC7 = 0.005 ± 0.007 (stat) ± 0.006(syst) at 7 TeV and ACCHC8 = 0.0055 ± 0.0023 (stat) ± 0.0025 (syst) at 8 TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the mathrm{t}overline{mathrm{t}} system at 8 TeV, are consistent with the respective standard model predictions.

Highlights

  • Collisions at the Tevatron, it is possible to define a forward-backward asymmetry AFB [1,2,3], while the same underlying physical effects induce a charge asymmetry AC in proton-proton collisions at the LHC [4, 5]

  • This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair events with a lepton+jets signature by the ATLAS and correlations from the ATLAS (CMS) Collaborations, using data from LHC proton-proton collisions at centreof-mass energies of 7 and 8 TeV

  • The NNLO prediction is based on the methods described in refs. [20, 22], derive√d using dynam√ical factorisation and renormalisation scales [21] (μ = HT/4, where HT = m2t + p2T,t + m2t + p2T,t, with mt being the top quark mass and pT,t/t being the transverse momentum of the top quark or antiquark) and a NNLO parton distribution function (PDF) set

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Summary

Introduction

Collisions at the Tevatron, it is possible to define a forward-backward asymmetry AFB [1,2,3], while the same underlying physical effects induce a charge asymmetry AC in proton-proton (pp) collisions at the LHC [4, 5]. Theoretical predictions from QCD calculations are available at next-to-leading-order (NLO) from refs. [4] and [19] and at next-to-next-to-leading-order (NNLO) [20,21,22,23] precision in the strong coupling These calculations include electroweak (EW) corrections at NLO precision. [4] uses a LO parton distribution function (PDF) set to evaluate the asymmetry, while the calculation in ref. [20, 22], derive√d using dynam√ical factorisation and renormalisation scales [21] (μ = HT/4, where HT = m2t + p2T,t + m2t + p2T,t, with mt being the top quark mass and pT,t/t being the transverse momentum of the top quark or antiquark) and a NNLO PDF set. In the NLO calculations, the ratio in eq (1.1) is evaluated in powers of the considered couplings (strong and electroweak), taking NLO corrections into account only in the numerator, while the denominator is evaluated with the LO matrix element

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