# Higgs-photon resonances

## TL;DR

This paper explores models predicting Higgs-photon resonances at the LHC, focusing on Z' bosons and scalars, analyzing their decay channels, observability, and potential for discovery in current and future experiments.

## Contribution

It introduces new models and scenarios for Higgs-photon resonances, including Z' and scalar cases, with detailed analysis of decay modes and experimental prospects.

## Key findings

- Z' decays to h^0 γ can have cross sections >1 fb for 200-450 GeV masses.
- Lepton pair decays of Z' compete with h^0 γ even without tree-level lepton couplings.
- Colimated photon pairs can mimic h^0 γ resonance, enabling discovery of heavier Z' up to 2 TeV.

## Abstract

We study models that produce a Higgs boson plus photon ($h^0 \gamma$) resonance at the LHC. When the resonance is a $Z'$ boson, decays to $h^0 \gamma$ occur at one loop. If the $Z'$ boson couples at tree-level to quarks, then the $h^0 \gamma$ branching fraction is typically of order $10^{-5}$ or smaller. Nevertheless, there are models that would allow the observation of $Z' \to h^0 \gamma$ at $\sqrt{s} = 13$ TeV with a cross section times branching fraction larger than 1 fb for a $Z'$ mass in the 200--450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The 1-loop decay of the $Z'$ into lepton pairs competes with $h^0 \gamma$, even if the $Z'$ couplings to leptons vanish at tree level. We also present a model in which a $Z'$ boson decays into a Higgs boson and a pair of collimated photons, mimicking an $h^0 \gamma$ resonance. In this model, the $h^0 \gamma$ resonance search would be the discovery mode for a $Z'$ as heavy as 2 TeV. When the resonance is a scalar, although decay to $h^0 \gamma$ is forbidden by angular momentum conservation, the $h^0$ plus collimated photons channel is allowed. We comment on prospects of observing an $h^0 \gamma$ resonance through different Higgs decays, on constraints from related searches, and on models where $h^0$ is replaced by a nonstandard Higgs boson.