Search for resonances in diphoton events at $\sqrt{s}$=13 TeV with the ATLAS detector

TL;DR

This paper reports on searches for new diphoton resonances at 13 TeV using ATLAS data, finding a local excess around 750 GeV with significance but no definitive discovery, and setting cross-section limits.

Contribution

First search for diphoton resonances at 13 TeV with ATLAS, exploring both spin-0 and spin-2 particles, and reporting potential excesses around 750 GeV.

Findings

Observed local significance of 3.8-3.9 sigma at 750 GeV

Global significance estimated at 2.1 sigma

Set limits on production cross section times branching ratio

Abstract

Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on proton--proton collision data corresponding to an integrated luminosity of 3.2 fb$^{-1}$ at $\sqrt{s} = 13$ TeV recorded in 2015. Two searches are performed, one targeted at a spin-2 particle of mass larger than 500 GeV, using Randall--Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle of mass larger than 200 GeV. Varying both the mass and the decay width, the most significant deviation from the background-only hypothesis is observed at a diphoton invariant mass around 750 GeV with local significances of 3.8 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 2.1 standard deviations for both analyses. The consistency between the data collected at 13 TeV and 8 TeV is also evaluated. Limits on the production cross section times branching ratio to two photons for the two resonance types are reported.