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

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.