Search for scalar diphoton resonances with 15.4~fb$^{-1}$ of data collected at $\sqrt{s}$=13 TeV in 2015 and 2016 with the ATLAS detector

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 corresponding to an integrated luminosity of 15.4 fb$^{-1}$ at $\sqrt{s}$=13~\TeV\ recorded in 2015 and 2016. 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. The global significance is estimated to be less than one standard deviation. Limits on the production cross section times branching ratio to two photons of such resonances are reported