NLO QCD corrections to off-shell ttbar production at hadron colliders

TL;DR

This paper presents a detailed NLO QCD calculation of off-shell top-antitop production at hadron colliders, including finite-width effects, to improve the precision of theoretical predictions for top-quark pair production and decay.

Contribution

It provides the first comprehensive NLO QCD analysis of the full pp -> W+ W- b bbar process with off-shell and finite-width effects, enhancing accuracy in top-quark studies.

Findings

Finite-top-width effects are at the percent level near resonances.

Off-shell tails can exhibit effects up to tens of percent.

Finite-W-width effects are generally below 0.5%.

Abstract

The production of top-antitop-quark pairs at hadron colliders is interesting both in its own right as signal process, but also as background to many searches for new physics. The corresponding predictions aim at the precision level of few per cent, rendering not only the inclusion of radiative corrections of the strong and electroweak interactions relevant, but also of off-shell and finite-width effects originating from the top-quark decays t -> b W -> b l \nu_l / qq'. We report on a calculation for the full process pp -> W^+ W^- b \bar{b} -> \nu_e e^+ \mu^- \nu_\mu b \bar{b} at next-to-leading order QCD and discuss the effects of the finite widths of the top quarks and of the W bosons for selected observables. Generically it turns out that finite-top-width effects are at the per-cent level whenever the top-quark resonances dominate, but those effects can reach tens of per cent in off-shell tails. Finite-W-width effects, on the other hand, are suppressed to less than 0.5% whenever the top quarks can become resonant and only become sizeable in exceptional cases. One such case, however, is the invariant mass of a bottom quark and the corresponding charged lepton, which result from the same top-quark decay - an observable that is relevant for precision measurements of the top-quark mass.