Inadequacy of zero-width approximation for a light Higgs boson signal

TL;DR

The paper demonstrates that the commonly used zero-width approximation for a light Higgs boson at the LHC can be inaccurate, emphasizing the importance of including off-shell effects for precise signal normalization.

Contribution

It shows that off-shell contributions significantly affect Higgs signal predictions, challenging the assumption that zero-width approximation is sufficient for light Higgs boson analyses.

Findings

Off-shell effects can cause ~10% corrections in Higgs signal normalization.

Sizable Higgs-continuum interference occurs in certain mass regions.

Experimental cuts can mitigate off-shell effects in some search channels.

Abstract

In the Higgs search at the LHC, a light Higgs boson (115 GeV <~ M_H <~ 130 GeV) is not excluded by experimental data. In this mass range, the width of the Standard Model Higgs boson is more than four orders of magnitude smaller than its mass. The zero-width approximation is hence expected to be an excellent approximation. We show that this is not always the case. The inclusion of off-shell contributions is essential to obtain an accurate Higgs signal normalisation at the 1% precision level. For gg (-> H) -> VV, V= W,Z, O(10%) corrections occur due to an enhanced Higgs signal in the region M_VV > 2 M_V, where also sizable Higgs-continuum interference occurs. We discuss how experimental selection cuts can be used to exclude this region in search channels where the Higgs invariant mass cannot be reconstructed. We note that the H -> VV decay modes in weak boson fusion are similarly affected.