Search for narrow scalar ${\mathrm{X}}\rightarrow \gamma\gamma$ in the mass range $65-600 \mathrm{\ Ge\kern -0.1em V}$ with the ATLAS detector

A search for scalar narrow resonance X decaying into two photons in the mass range 65-600 $\mathrm{\ Ge\kern -0.1em V}$ is performed using 20 fb$^{-1}$ of $pp$ collision data collected with the ATLAS detector at $\sqrt{s}$ = 8 $\mathrm{\ Te\kern -0.1em V}$ at the Large Hadron Collider. The signal associated to the diphoton decay of the Higgs boson with a mass of $125.9\mathrm{\ Ge\kern -0.1em V}$ is treated as a background. No significant evidence for an additional signal is observed. The result is presented as a model-independent limit on the production cross-section times the branching fraction BR ($\mathrm{X}\rightarrow \gamma\gamma$), in a fiducial volume where the reconstruction efficiency is independent of the event topology. The upper limits set extend over a considerably wider mass range than for the limits previously set by the ATLAS and CMS collaborations.