Revealing the electroweak properties of a new scalar resonance

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: W + W − , ZZ, γγ, and Zγ. 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 W + W − or very enhanced branchings to γγ and Zγ. 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.

Light signals from a lighter Higgs

“…A simple example is that of a singlet scalar, φ, which has been extensively discussed (see e.g., [5][6][7][8][9][10][11][12]). To allow for production from gluon fusion at the LHC the singlet must couple to extra vectorlike colored matter, yφΨΨ, necessitating the introduction of many new degrees of freedom.…”

Coupling spans of the Higgs-like boson

“…2 In many models, the h 0 W W coupling is substantially smaller than in the SM, and only in the unusual case [25][26][27][28][29][30] of large VEVs for higher SU(2) W representations does the coupling exceed its SM value. 3 We then translate this limit on Γ h into an upper limit on the exotic branching fraction, B X .…”

“…Nevertheless, new physics contributions may still have effects larger than 50% on some of these couplings. [27][28][29], but models of this type include several charged particles that can be ruled out or discovered at the LHC in the near future.…”

Singlet scalars as Higgs boson imposters at the Large Hadron Collider

“…4 In the SM the m W → ∞ limit is not valid; we are interested in this limit only in the context of understanding the coupling of S. 5 Here we see explicitly that the top quark, or any fourth generation fermion, interferes destructively with the W boson loop. In the plot we assume the production rate of S is the same as that of a SM Higgs with the same mass.…”

“…[4], a particularly interesting candidate for a Higgs imposter is a massive spin zero particle transforming as a SM singlet. (See also Refs.…”