Gluon-induced W-boson pair production at the LHC

TL;DR

This paper delivers the first complete calculation of the loop-induced gluon-fusion background to $W$-pair production at the LHC, evaluating $gg \to W^{*}W^{*} \to \ell\bar{\nu}\bar{\ell'}\nu'$ with full light and heavy quark mass effects and arbitrary $W$ virtualities, including the top-bottom quark loop and Higgs-mediated contributions. The authors develop a robust analytic-numeric framework using algebraic tensor reduction to maintain gauge invariance and numerical stability, complemented by a mixed-precision strategy and public code (GG2WW) for differential predictions and event generation. They find that the top-bottom loop enhances the inclusive gluon-induced cross section by about $12$–$15\%$, but this effect largely disappears under Higgs-search cuts (down to ~$2\%$) due to kinematic selections, notably $\ abla\phi_{T,\ell\ell}$. Interference between signal and gluon-induced background is small (<$5\%$) across the studied Higgs masses, implying the gluon contribution is an important, though controlled, higher-order background. Overall, GG2WW provides precise, differential predictions essential for Higgs analyses and background modeling at the LHC.

Abstract

Pair production of W bosons constitutes an important background to Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons, including intermediate light and heavy quarks and allowing for arbitrary invariant masses of the W bosons. While formally of next-to-next-to-leading order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at the LHC and by experimental Higgs search cuts, and increases the next-to-leading order WW background estimate for Higgs searches by about 30%. We have extended our previous calculation to include the contribution from the intermediate top-bottom massive quark loop and the Higgs signal process. We provide updated results for cross sections and differential distributions and study the interference between the different gluon scattering contributions. We describe important analytical and numerical aspects of our calculation and present the public GG2WW event generator.