The 750 GeV threshold to a new particle world

TL;DR

This paper proposes that the 750 GeV diphoton excess observed at the LHC could be explained by a threshold effect from virtual production of extra quark pairs, rather than a new resonance.

Contribution

It introduces a novel interpretation of the diphoton excess as a threshold effect involving virtual quark pairs, challenging the resonance hypothesis.

Findings

The 750 GeV excess can be explained without a new resonance.

Threshold effects from virtual quark pairs can produce observable diphoton signals.

This interpretation aligns with the 2015 excess data but not with 2016 data.

Abstract

We show how an excess in the diphoton channel can be the effect of neither a resonance nor an end-point in a cascade decay, but rather of a threshold for virtual production of a pair of extra quarks, each with half of peak invariant mass, onsetting in both the $gg$-initiated production and the $\gamma\gamma$-induced decay of an off-shell $Z$ boson. For our analysis we consider as paradigmatic example the 750 GeV excess previously seen at the end of 2015 with the Run 2 data of the LHC but not confirmed with 2016 data.