NLO QCD corrections to off-shell ${t\bar{t}W^\pm}$ production at the LHC: Correlations and Asymmetries

TL;DR

This paper provides precise NLO QCD predictions for off-shell top-antitop-W production at the LHC, focusing on cross section ratios and charge asymmetries to better understand potential new physics effects.

Contribution

It introduces full off-shell NLO QCD calculations for ${t\bar{t}W^{\pm}}$ production, improving theoretical precision for key observables relevant to new physics searches.

Findings

Achieves 2-3% precision on the cross section ratio ${\cal R}$.

Obtains below 15% uncertainties on charge asymmetries.

Reveals the impact of top decay modeling on asymmetry predictions.

Abstract

Recent discrepancies between theoretical predictions and experimental data in multi-lepton plus $b$-jets analyses for the $t\bar{t}W^\pm$ process, as reported by the ATLAS collaboration, have indicated that more accurate theoretical predictions and high precision observables are needed to constrain numerous new physics scenarios in this channel. To this end we employ NLO QCD computations with full off-shell top quark effects included to provide theoretical predictions for the ${\cal R}= \sigma_{t\bar{t}W^+}/\sigma_{t\bar{t}W^-}$ cross section ratio at the LHC with $\sqrt{s}=13$ TeV. Depending on the transverse momentum cut on the $b$-jet we obtain $2\% -3 \%$ theoretical precision on ${\cal R}$, which should help to shed some light on new physics effects that can reveal themselves only once sufficiently precise Standard Model theoretical predictions are available. Furthermore, triggered by these discrepancies we reexamine the charge asymmetry of the top quark and its decay products in the $t\bar{t}W^\pm$ production process. In the case of charge asymmetries, that are uniquely sensitive to the chiral nature of possible new physics in this channel, theoretical uncertainties below $15\%$ are obtained. Additionally, the impact of the top quark decay modelling is scrutinised by explicit comparison with predictions in the narrow-width approximation.