Probing a virtual diphoton excess

Abstract

Interpreting the excesses around 750 GeV in the diphoton spectra to be the signal of a new heavy scalar φ decaying to photons, we point out the possibility of looking for correlated signals with virtual photons. In particular, we emphasize that the effective operator that generates the φ→γγ decay will also generate decays of φ→2ℓγ (2ℓ≡2e,2ν) and φ→4ℓ (4ℓ≡2e2μ,4e,4μ) independently of the φ couplings to Zγ and ZZ. Depending on the relative sizes of these effective couplings, we show that the virtual diphoton component can make up a sizable, and sometimes dominant, contribution to the total φ→2ℓγ and φ→4ℓ partial widths. We also discuss modifications to current experimental cuts in order to maximize the sensitivity to these virtual photon effects. Finally, we briefly comment on prospects for channels involving other Standard Model fermions as well as more exotic decay possibilities of the putative resonance.