Wide or Narrow? The Phenomenology of 750 GeV Diphotons

TL;DR

This paper combines ATLAS and CMS diphoton data to analyze the 750 GeV anomaly, finding increased significance for a spin-0 mediator and disfavoring a spin-2 hypothesis, with detailed cross section and width considerations.

Contribution

It provides a combined analysis of Run-I and Run-II diphoton data, strengthening the statistical significance of the 750 GeV anomaly and comparing spin hypotheses with detailed cross section fits.

Findings

Combined data increases anomaly significance to 4.0σ for spin-0 mediator.

Spin-2 mediator is disfavored compared to spin-0.

Best fit cross section is around 4 fb at 13 TeV for narrow width.

Abstract

I perform a combined analysis of the ATLAS and CMS diphoton data, using both Run-I and Run-II results, including those released at the 2016 Moriond conference. I find combining the ATLAS and CMS results from Run-II increases the statistical significance of the reported 750 GeV anomaly, assuming a spin-0 mediator coupling to gluons or heavy quarks with a width much smaller than the detector resolution. This significance does not decrease when the 8 TeV data is included. A spin-2 mediator is disfavored compared to the spin-0 case. The cross section required to fit the ATLAS anomaly is in tension with the aggregate data, all of which prefers a smaller value. The best fit for all models I consider is a $4.0\sigma$ local significance for a 750 GeV spin-0 mediator coupling to gluons with a cross section of 4 fb at 13 TeV (assuming narrow width) or 10~fb (assuming $\Gamma=45$ GeV).