NLO QCD corrections to off-shell top-antitop production with leptonic decays at hadron colliders

TL;DR

This paper provides a detailed NLO QCD calculation of off-shell top-antitop production with leptonic decays at hadron colliders, including non-resonant and off-shell effects, and introduces a matching approach for unstable particles.

Contribution

It presents a comprehensive NLO QCD calculation including off-shell effects and non-resonant diagrams, with a new matching method for unstable particles and improved scale choices for stability.

Findings

Off-shell and non-resonant effects are small in inclusive cross sections but significant in exclusive observables.

A dynamical scale stabilizes NLO predictions in high-energy tails.

Numerical results for total cross sections and distributions at Tevatron and LHC energies are provided.

Abstract

We present details of a calculation of the cross section for hadronic top-antitop production in next-to-leading order (NLO) QCD, including the decays of the top and antitop into bottom quarks and leptons. This calculation is based on matrix elements for \nu e e+ \mu- \bar{\nu}_{\mu}b\bar{b} production and includes all non-resonant diagrams, interferences, and off-shell effects of the top quarks. Such contributions are formally suppressed by the top-quark width and turn out to be small in the inclusive cross section. However, they can be strongly enhanced in exclusive observables that play an important role in Higgs and new-physics searches. Also non-resonant and off-shell effects due to the finite W-boson width are investigated in detail, but their impact is much smaller than naively expected. We also introduce a matching approach to improve NLO calculations involving intermediate unstable particles. Using a fixed QCD scale leads to perturbative instabilities in the high-energy tails of distributions, but an appropriate dynamical scale stabilises NLO predictions. Numerical results for the total cross section, several distributions, and asymmetries are presented for Tevatron and the LHC at 7 TeV, 8 TeV, and 14 TeV.