# Dissecting Multi-Photon Resonances at the Large Hadron Collider

## TL;DR

This paper explores how multi-photon resonances at the LHC can mimic two-photon signals due to collinear decay photons, proposing photon jet substructure analysis to distinguish scenarios and infer particle properties.

## Contribution

It introduces a method using photon jet substructure variables to differentiate multi-photon decay scenarios from direct two-photon decays at the LHC.

## Key findings

- Photon jet substructure helps distinguish multi-photon from two-photon signals.
- Pseudorapidity gap distributions reveal spin information of particles.
- Photon jet mass analysis provides insights into the mass of intermediate particles.

## Abstract

We examine the phenomenology of the production, at the 13 TeV Large Hadron Collider (LHC), of a heavy resonance $X$, which decays via other new on-shell particles $n$ into multi- (i.e.\ three or more) photon final states. In the limit that $n$ has a much smaller mass than $X$, the multi-photon final state may dominantly appear as a two photon final state because the $\gamma$s from the $n$ decay are highly collinear and remain unresolved. We discuss how to discriminate this scenario from $X \rightarrow \gamma \gamma$: rather than discarding non-isolated photons, it is better instead to relax the isolation criterion and instead form photon jet substructure variables. The spins of $X$ and $n$ leave their imprint upon the distribution of pseudorapidity gap $\Delta \eta$ between the apparent two photon states. Depending on the total integrated luminosity, this can be used in many cases to claim discrimination between the possible spin choices of $X$ and $n$, although the case where $X$ and $n$ are both scalar particles cannot be discriminated from the direct $X \rightarrow \gamma \gamma$ decay in this manner. Information on the mass of $n$ can be gained by considering the mass of each photon jet.