Gluon-induced WW background to Higgs boson searches at the LHC

TL;DR

This work addresses the accuracy of the $WW$ background to Higgs searches in the $pp \to H \to W^{*}W^{*} \to \ell\bar{\nu}\bar{\ell'}\nu'$ channel by computing the loop-induced process $gg \to W^{*}W^{*} \to \ell\bar{\nu}\bar{\ell'}\nu'$. It presents a full calculation with off-shell $W$ bosons, spin correlations, and arbitrary invariant masses, using massless light-quark loops and two independent, numerically stable tensor-reduction approaches. The results show that while $gg$-initiated $WW$ production is only about a 5% correction to the inclusive $WW$ cross section, it increases the Higgs-background estimate by ~30% after realistic Higgs-selection cuts, indicating a sizable impact on Higgs discovery potential. The study underscores the necessity of including gluon-induced backgrounds in LHC analyses and provides a robust methodological framework for precise background modeling in $H\to WW$ searches.

Abstract

Vector-boson pair production is an important background for Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg -> WW -> leptons, allowing for arbitrary invariant masses of the intermediate W bosons. This process contributes at O(alpha_s^2) relative to quark-antiquark annihilation, but its importance is enhanced by the large gluon flux at the LHC and by experimental cuts employed in Higgs boson searches. We find that gg -> WW provides only a moderate correction (ca. 5%) to the inclusive W-pair production cross section at the LHC. However, after taking into account realistic experimental cuts, the gluon-fusion process becomes significant and increases the theoretical WW background estimate for Higgs searches in the pp -> H -> WW -> leptons channel by approximately 30%.