On the excess in the inclusive $W^+W^-\rightarrow l^+l^-\nu\bar\nu$ cross section

TL;DR

This paper investigates the reported excess in the inclusive $W^+W^-$ cross section at the LHC, finding that the fiducial measurements align with NLO QCD predictions and that higher-order corrections are unlikely to resolve the observed discrepancies.

Contribution

It clarifies that the excess is not present in fiducial cross sections and highlights the impact of extrapolation methods on total cross section measurements.

Findings

Fiducial cross sections agree with NLO QCD predictions.

Higher order effects are small and tend to cancel.

Extrapolation with POWHEG influences the total cross section discrepancy.

Abstract

In this note we analyse the excess in the $W^+W^-$ inclusive cross section recently measured by the LHC experiments. We point out that in fact for the ATLAS fiducial cross sections there is no excess in the measurements compared to the NLO QCD predictions. We also argue that higher order effects to the fiducial cross section are small, and tend to cancel each other, hence the inclusion of NNLO and NNLL corrections will not modify this agreement significantly. We find that at 8 TeV a substantial part of the disagreement with the NLO prediction for the total cross section observed by ATLAS is due to the extrapolation carried out with POWHEG.