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Visible Cascade Higgs Decays to Four Photons at Hadron Colliders

Spencer Chang, Patrick J. Fox, Neal Weiner

TL;DR

The paper investigates cascade Higgs decays h→2a mediated by a new CP-odd pseudoscalar a, which can drastically alter Higgs phenomenology and undermine standard SM search channels. It analyzes the loop-induced decays a→gg and a→γγ via heavy vectorlike fermions, focusing on the clean h→4γ final state as a potential universal discovery channel for both h and a. Through a parton-level collider study with realistic photon cuts and backgrounds, it shows that the LHC could discover such a Higgs with BR(h→4γ) ≈ 10^-4 for a wide range of masses, whereas the Tevatron requires BR ≳ a few×10^-3 and is more constrained by LEP limits. The work highlights the importance of photon-based triggers and background suppression, and it discusses possible displaced-decay scenarios of a that could further influence experimental strategies.

Abstract

The presence of a new singlet scalar particle a can open up new decay channels for the Higgs boson, through cascades of the form h -> 2a -> X, possibly making discovery through standard model channels impossible. If a is CP-odd, its decay products are particularly sensitive to physics beyond the standard model. Quantum effects from heavy fields can naturally make gluonic decay, a -> 2g, the dominant decay mode, resulting in a h -> 4 g decay which is difficult to observe at hadron colliders, and is allowed by LEP for m_h > 82 GeV. However, there are usually associated decays with photons, either h -> 2g 2gamma or h -> 4gamma, which are more promising. The decay h -> 2g 2gamma only allows discovery of the a particle and not the Higgs whereas h -> 4gamma is a clean channel that can discover both particles. We determine what branching ratios are required for discovery at LHC and find that with 300 fb^-1 of luminosity, a branching ratio of order 10^-4 is sufficient for a large region of Higgs masses. Due to a lower expected luminosity of ~ 8 fb^-1, discovery at the Tevatron requires more than 5 x 10^-3 in branching ratio.

Visible Cascade Higgs Decays to Four Photons at Hadron Colliders

TL;DR

The paper investigates cascade Higgs decays h→2a mediated by a new CP-odd pseudoscalar a, which can drastically alter Higgs phenomenology and undermine standard SM search channels. It analyzes the loop-induced decays a→gg and a→γγ via heavy vectorlike fermions, focusing on the clean h→4γ final state as a potential universal discovery channel for both h and a. Through a parton-level collider study with realistic photon cuts and backgrounds, it shows that the LHC could discover such a Higgs with BR(h→4γ) ≈ 10^-4 for a wide range of masses, whereas the Tevatron requires BR ≳ a few×10^-3 and is more constrained by LEP limits. The work highlights the importance of photon-based triggers and background suppression, and it discusses possible displaced-decay scenarios of a that could further influence experimental strategies.

Abstract

The presence of a new singlet scalar particle a can open up new decay channels for the Higgs boson, through cascades of the form h -> 2a -> X, possibly making discovery through standard model channels impossible. If a is CP-odd, its decay products are particularly sensitive to physics beyond the standard model. Quantum effects from heavy fields can naturally make gluonic decay, a -> 2g, the dominant decay mode, resulting in a h -> 4 g decay which is difficult to observe at hadron colliders, and is allowed by LEP for m_h > 82 GeV. However, there are usually associated decays with photons, either h -> 2g 2gamma or h -> 4gamma, which are more promising. The decay h -> 2g 2gamma only allows discovery of the a particle and not the Higgs whereas h -> 4gamma is a clean channel that can discover both particles. We determine what branching ratios are required for discovery at LHC and find that with 300 fb^-1 of luminosity, a branching ratio of order 10^-4 is sufficient for a large region of Higgs masses. Due to a lower expected luminosity of ~ 8 fb^-1, discovery at the Tevatron requires more than 5 x 10^-3 in branching ratio.

Paper Structure

This paper contains 4 sections, 6 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Higgs decays to scalars
  3. Detection prospects at colliders
  4. Conclusions

Figures (2)

  • Figure 1: LHC background under the cuts given in the text, in femtobarns, binned in 5 GeV windows for both the candidate $m_h$ and $m_a$. There is no point with value above $10^{-4}$.
  • Figure 2: Branching ratios sufficient for discovery ($\geq 5$ signal events), given 300 $\,{\rm fb}^{-1}$ of integrated luminosity at LHC. The bottom region is cut off by the lack of photon isolation, and we consider the region up to $m_h \le 160 \,{\rm GeV}$, above which we expect $W^+W^-$ decays to dominate.