# Interference in the $gg\rightarrow h \rightarrow \gamma\gamma$ On-Shell Rate and the Higgs Boson Total Width

## TL;DR

This paper investigates how interference effects between the Higgs signal and background in gluon fusion impact the on-shell Higgs rate and how this can be used to indirectly measure the Higgs boson total width, especially with future collider data.

## Contribution

It introduces the significance of interference effects in Higgs measurements and proposes a novel method to constrain the Higgs width using on-shell rate data, considering potential BSM enhancements.

## Key findings

- Interference causes about 2% destructive effect on the on-shell rate in the SM.
- Interference effects can be amplified by BSM physics, affecting width measurements.
- HL-LHC could indirectly measure Higgs widths down to tens of MeV.

## Abstract

We consider interference between the Higgs signal and QCD background in $gg\rightarrow h \rightarrow \gamma\gamma$ and its effect on the on-shell Higgs rate. The existence of sizable strong phases leads to destructive interference of about 2% of the on-shell cross section in the Standard Model. This effect can be enhanced by beyond the standard model physics. In particular, since it scales differently from the usual rates, the presence of interference allows indirect limits to be placed on the Higgs width in a novel way, using on-shell rate measurements. Our study motivates further QCD calculations to reduce uncertainties. We discuss potential width-sensitive observables, both using total and differential rates and find that the HL-LHC can potentially indirectly probe widths of order tens of MeV.