Resonances from QCD bound states and the 750 GeV diphoton excess

TL;DR

This paper explores the possibility that the 750 GeV diphoton excess observed in experiments could be explained by QCD bound states of new colored particles, updating previous estimates with recent data.

Contribution

It provides an updated analysis of bound state signals for new colored particles, suggesting they could explain the 750 GeV diphoton excess and identifying specific candidate particles.

Findings

A narrow resonance near 375 GeV could explain the 750 GeV excess.

Certain colored scalar and fermion particles are viable candidates.

Updated bounds from 8 and 13 TeV data support the bound state explanation.

Abstract

Pair production of colored particles is in general accompanied by production of QCD bound states (onia) slightly below the pair-production threshold. Bound state annihilation leads to resonant signals, which in some cases are easier to see than the decays of the pair-produced constituents. In a previous paper (arXiv:1204.1119) we estimated the bound state signals, at leading order and in the Coulomb approximation, for particles with various spins, color representations and electric charges, and used 7 TeV ATLAS and CMS resonance searches to set rough limits. Here we update our results to include 8 and 13 TeV data. We find that the recently reported diphoton excesses near 750 GeV could indeed be due to a bound state of this kind. A narrow resonance of the correct size could be obtained for a color-triplet scalar with electric charge -4/3 and mass near 375 GeV, if (as a recent lattice computation suggests) the wave function at the origin is somewhat larger than anticipated. Pair production of this particle could have evaded detection up to now. Other candidates may include a triplet scalar of charge 5/3, a triplet fermion of charge -4/3, and perhaps a sextet scalar of charge -2/3.