Dissecting multi-photon resonances at the large hadron collider

Abstract

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 $$\gamma $$ γ s from the n decay are highly collinear and remain unresolved. We discuss how to discriminate this scenario from $$X \rightarrow \gamma \gamma $$ X → γ γ : rather than discarding non-isolated photons, it is better to relax the isolation criteria and instead form photon jets substructure variables. The spins of X and n leave their imprint upon the distribution of pseudo-rapidity gap $$\Delta \eta $$ Δ η 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 $$X \rightarrow \gamma \gamma $$ X → γ γ decay in this manner. Information on the mass of n can be gained by considering the mass of each photon jet.