Revealing the electroweak properties of a new scalar resonance

TL;DR

This paper discusses how to determine the electroweak properties of a new scalar resonance discovered at the LHC by analyzing its decay rates into electroweak vector bosons, helping distinguish it from the Standard Model Higgs.

Contribution

It provides a model-independent framework for identifying the electroweak quantum numbers of a new scalar resonance using decay mode measurements, considering operators up to dimension five.

Findings

Only four decay pattern cases need to be distinguished.

Measurement of all four decay modes can identify the resonance's nature.

Special decay patterns can mimic the Standard Model Higgs, requiring detailed analysis.

Abstract

One or more new heavy resonances may be discovered in experiments at the CERN Large Hadron Collider. In order to determine if such a resonance is the long-awaited Higgs boson, it is essential to pin down its spin, CP, and electroweak quantum numbers. Here we describe how to determine what role a newly-discovered neutral CP-even scalar plays in electroweak symmetry breaking, by measuring its relative decay rates into pairs of electroweak vector bosons: WW, ZZ, \gamma\gamma, and Z\gamma. With the data-driven assumption that electroweak symmetry breaking respects a remnant custodial symmetry, we perform a general analysis with operators up to dimension five. Remarkably, only three pure cases and one nontrivial mixed case need to be disambiguated, which can always be done if all four decay modes to electroweak vector bosons can be observed or constrained. We exhibit interesting special cases of Higgs look-alikes with nonstandard decay patterns, including a very suppressed branching to WW or very enhanced branchings to \gamma\gamma and Z\gamma. Even if two vector boson branching fractions conform to Standard Model expectations for a Higgs doublet, measurements of the other two decay modes could unmask a Higgs imposter.