Limitations and Opportunities of Off-Shell Coupling Measurements

TL;DR

This paper critically examines the reliability of using off-shell Higgs measurements to constrain the Higgs width, highlighting the need for model-specific assumptions and exploring alternative high-energy analysis methods.

Contribution

It provides a new perspective on off-shell Higgs width constraints, emphasizing the limitations of current methods and proposing more model-independent approaches for future analyses.

Findings

Limits on Higgs width from off-shell measurements are unreliable without model assumptions.

High invariant mass cross section measurements can inform Higgs CP and new physics studies.

A model-independent LHC constraint can be derived from weak boson fusion channel analyses.

Abstract

Indirect constraints on the total Higgs width $\Gamma_h$ from correlating Higgs signal strengths with cross section measurements in the off-shell region for $p(g)p(g)\to 4\ell$ production have received considerable attention recently, and the CMS collaboration have published a first measurement. We revisit this analysis from a new physics and unitarity constraints perspective and conclude that limits on $\Gamma_h$ obtained in this fashion are not reliable unless we make model-specific assumptions, which cannot be justified at the current stage of the LHC programme. Relaxing the $\Gamma_h$ interpretation, we discuss the merits of high invariant mass cross section measurements in the context of Higgs CP analyses, higher dimensional operator testing, and resolved new physics in the light of electroweak precision constraints beyond effective theory limitations. Furthermore, we show that a rather model-independent LHC constraint can be obtained from adapting the $gg\to 4\ell$ analysis to the weak boson fusion channels at lower statistical yield.