Precise predictions for same-sign W-boson scattering at the LHC

TL;DR

This paper provides a comprehensive analysis of same-sign W-boson scattering at the LHC, comparing various approximations and NLO QCD predictions to improve theoretical precision for experimental measurements.

Contribution

It systematically compares approximations against complete calculations and assesses the impact of NLO QCD corrections and parton-shower matching on predictions.

Findings

NLO QCD corrections stabilize predictions.

Differences in approximations are significant in inclusive regions.

Parton-shower effects cause larger variations than fixed-order calculations.

Abstract

Vector-boson scattering processes are of great importance for the current run-II and future runs of the Large Hadron Collider. The presence of triple and quartic gauge couplings in the process gives access to the gauge sector of the Standard Model (SM) and possible new-physics contributions there. To test any new-physics hypothesis, sound knowledge of the SM contributions is necessary, with a precision which at least matches the experimental uncertainties of existing and forthcoming measurements. In this article we present a detailed study of the vector-boson scattering process with two positively-charged leptons and missing transverse momentum in the final state. In particular, we first carry out a systematic comparison of the various approximations that are usually performed for this kind of process against the complete calculation, at LO and NLO QCD accuracy. Such a study is performed both in the usual fiducial region used by experimental collaborations and in a more inclusive phase space, where the differences among the various approximations lead to more sizeable effects. Afterwards, we turn to predictions matched to parton showers, at LO and NLO: we show that on the one hand, the inclusion of NLO QCD corrections leads to more stable predictions, but on the other hand the details of the matching and of the parton-shower programs cause differences which are considerably larger than those observed at fixed order, even in the experimental fiducial region. We conclude with recommendations for experimental studies of vector-boson scattering processes.