Dissecting multi-photon resonances at the large hadron collider.

We examine the phenomenology of the production, at the 13 TeV Large Hadron Collider (LHC), of a heavy resonance , which decays via other new on-shell particles into multi-(i.e. three or more) photon final states. In the limit that has a much smaller mass than , the multi-photon final state may dominantly appear as a two-photon final state because the s from the decay are highly collinear and remain unresolved. We discuss how to discriminate this scenario from : rather than discarding non-isolated photons, it is better to relax the isolation criteria and instead form photon jets substructure variables. The spins of and leave their imprint upon the distribution of pseudo-rapidity gap 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 and , although the case where and are both scalar particles cannot be discriminated from the direct decay in this manner. Information on the mass of can be gained by considering the mass of each photon jet.