Gluon-gluon contributions to W+ W- production and Higgs interference effects

TL;DR

This paper calculates gluon-gluon contributions to W+ W- production at the LHC, including Higgs interference effects, revealing significant impacts on Higgs search signals and proposing optimized cuts to improve detection accuracy.

Contribution

It provides the first analytic calculation of gg -> W+ W- including massive quark loops and quantifies Higgs interference effects on W pair production at the LHC.

Findings

Gluon-gluon contributions can cause about 10% reduction in Higgs signal events for mH < 140 GeV.

Interference effects are largely reduced to about 1% with current transverse mass cuts.

Proposes using a maximum transverse mass cut to improve Higgs search sensitivity.

Abstract

In this paper we complete our re-assessment of the production of W boson pairs at the LHC, by calculating analytic results for the gg -> W+ W- -> (\nu l l\nu) process including the effect of massive quarks circulating in the loop. Together with the one-loop amplitudes containing the first two generations of massless quarks propagating in the loop, these diagrams can give a significant contribution with a large flux of gluons. One of the component parts of this calculation is the production of a standard model Higgs boson, gg -> H and its subsequent decay, H -> W+(-> \nu l) W-(-> l \nu). We will quantify the importance of the interference between the Higgs boson production process and the gluon-induced continuum production in the context of searches for the Higgs boson at the Tevatron and the LHC. For instance, for mH < 140 GeV the effect of the interference typically results in around a 10% reduction in the expected number of Higgs signal events. The majority of this interference is due to non-resonant contributions. Therefore cuts on the transverse mass such as those currently used by the ATLAS collaboration reduce the destructive interference to about a 1% effect. We advocate that a cut on the maximum transverse mass be used in future Higgs searches in this channel.