On-shell interference effects in Higgs final states

TL;DR

This paper investigates how on-shell interference effects from top quark loops affect Higgs boson searches at large invariant masses, revealing significant modifications to signal strength estimates.

Contribution

It provides the first detailed analysis of on-shell interference effects in Higgs to ZZ processes, highlighting their impact on experimental signal interpretations.

Findings

Interference effects can modify signal strength by up to 30%.

Including continuum contributions reduces the modification to about 10%.

Effects are scheme-dependent and relevant for broad heavy scalars.

Abstract

Top quark loops in Higgs production via gluon fusion at large invariant final state masses can induce important interference effects in searches for additional Higgs bosons as predicted in, e.g., Higgs portal scenarios and the MSSM when the heavy scalar is broad or the final state resolution is poor. Currently, the limit setting as performed by both ATLAS and CMS is based on injecting a heavy Higgs-like signal neglecting interference effects. In this paper, we perform a study of such "on-shell" interference effects in $pp\to ZZ$ and find that they lead to a $\lesssim{\cal{O}}(30%)$ width scheme-dependent modification of the signal strength. Including the continuum contributions to obtain e.g. the full $pp\to ZZ \to 4\ell$ final state, this modification is reduced to the 10% level in the considered intermediate mass range.