The 750 GeV $S$-cion: Where else should we look for it?

TL;DR

This paper explores alternative search channels for the 750 GeV diphoton resonance, proposing new LHC signatures and analyzing their potential to reveal new physics related to this excess.

Contribution

It introduces a framework for searching for the 750 GeV resonance in channels like $\gamma\gamma\ell\ell$, $\gamma\gamma\ell otackslash$, and $\ell\ell\ell\gamma otackslash$, and discusses models with vector-like fermions.

Findings

LHC could detect excesses in $\gamma\gamma\ell\ell$ with 3 fb$^{-1}$

Potential for 5σ discovery with 65 fb$^{-1}$ in $\ell\ell\ell\gamma otackslash$ channel

Models with heavy vector-like quarks/leptons can fit the diphoton excess and be discovered in proposed channels.

Abstract

The resonance $S$ at $\sim 750$ GeV in the diphoton channel observed by ATLAS and CMS, if it holds up, is almost certainly the ($S$)cion of a larger dynasty in a UV completion that may very well be connected to the hierarchy problem. At this stage, however, an effective field theory framework provides a useful way to parametrize searches for this resonance in other channels. Assuming that the excess is due to a new scalar or pseudoscalar boson, we study associated production of $S$ ("$S$-strahlung") at the LHC and propose searches in several clean channels like $\gamma\gamma\ell\ell$, $\gamma\gamma\ell\eslash$ and $\ell\ell\ell\gamma\eslash$ to probe dimension-5 operators coupling $S$ to Standard Model gauge bosons. We consider a range of widths for $S$, from 5 GeV to 45 GeV, and find that the three channels probe complementary regions of parameter space and the suppression scale $\Lambda$. The finding of most immediate relevance is that with 3 fb$^{-1}$, the LHC might already reveal new excesses in the $\gamma\gamma\ell\ell$ channel and a 5(3) $\sigma$ discovery may already be possible after collecting 65(25) fb$^{-1}$ of data with $\ell\ell\ell\gamma\eslash$ events if the scale of the new physics is within $\sim $ 9 TeV for couplings respecting 8 TeV LHC bounds and compatible with the observed excess in diphotons for a wide resonance as suggested by the ATLAS Collaboration. Beyond the EFT parametrization, we found realizations of models with heavy vector-like quarks and leptons which can simultaneously fit the diphoton excess and be discovered in the channels proposed here.