The Virtual Diphoton Excess

TL;DR

This paper explores the potential for detecting signals of a new 750 GeV scalar resonance through virtual photon processes, which could significantly contribute to multi-lepton and photon final states, offering new experimental search avenues.

Contribution

It introduces the idea that virtual photon decays of the resonance can be sizable and sometimes dominant, suggesting new strategies for experimental detection beyond direct diphoton signals.

Findings

Virtual photon decays can significantly contribute to 2-lepton + photon final states.

Virtual photon effects may dominate the 4-lepton decay channel.

Modifications to experimental cuts can enhance sensitivity to virtual photon signals.

Abstract

Interpreting the excesses around 750 GeV in the diphoton spectra to be the signal of a new heavy scalar 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 diphoton decay will also generate decays to two leptons and a photon, as well as to four leptons, independently of the new resonance couplings to $Z\gamma$ 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 $2\ell \gamma$ and $4\ell$ 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.