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

TL;DR

This paper investigates the charge asymmetry and polarization effects in top-antitop quark production with an associated W boson at the LHC, revealing enhanced asymmetries and polarization signals compared to inclusive top pair production.

Contribution

It demonstrates that $t\bar{t}W^{\pm}$ production exhibits larger charge asymmetries and polarization effects at NLO in QCD due to initial-state quark dominance, providing new insights for experimental measurements.

Findings

Charge asymmetry is significantly larger in $t\bar{t}W^{\pm}$ than in inclusive $t\bar{t}$ production.

Top quark polarization inherits initial-state quark polarization, leading to observable asymmetries.

Distributions and uncertainties are analyzed within the Standard Model and a simple axigluon model.

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.