Search for a high mass diphoton resonance using the ATLAS detector

Abstract: A search for new spin-0 resonances decaying into two photons in the ATLAS experiment at the LHC is described. The analysis is based on $pp$ collision data at $\sqrt{s}$=13 TeV corresponding to integrated luminosities of 3.2/fb and 12.2/fb recorded in 2015 and 2016, respectively. A deviation from the Standard Model background-only hypothesis corresponding to 3.4 standard deviations is observed in the 2015 data for a resonance mass hypothesis of 730 GeV. No significant excess at such mass over the background expectation is observed in the 2016 data. Limits on the production cross section times branching ratio to two photons of such resonances are reported.