Top-quark charge asymmetry and polarization in $t\bar{t}{W}^{\pm }$ production at the LHC

Abstract

We study the charge asymmetry between the $t$ and $\bar{t}$ quark 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, $t\bar{t}{W}^{\pm }$ production can only occur via $q\bar{q}$ annihilation. As a result, the asymmetry between the $t$ and $\bar{t}$ generated at NLO in QCD is significantly larger than that of inclusive $t\bar{t}$ 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.

11 pages (with figures), version accepted by PLB for publication

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• The simplest of them all: $t\bar{t}{W}^{\pm }$ at NLO accuracy in QCD
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