Top-quark charge asymmetry and polarization in tt¯W± production at the LHC

Abstract

We study the charge asymmetry between the t and t¯ quarks at the LHC, when they are produced in association with a W boson. Though sizably reducing the cross section with respect to the inclusive production, requiring a W boson in the final state has two important implications. First, at leading order in QCD, tt¯W± production can only occur via qq¯ annihilation. As a result, the asymmetry between the t and t¯ generated at NLO in QCD is significantly larger than that of inclusive tt¯ production, which is dominated by gluon fusion. Second, the top quarks tend to inherit the polarization of the initial-state quarks as induced by the W-boson emission. Hence, the decay products of the top quarks display a sizable asymmetry already at the leading order in QCD. We study the relevant distributions and their uncertainties in the standard model, compare them to those obtained in a simple axigluon model and discuss prospects for measurements at the LHC and beyond.