Search for resonances in the 65 to 110 GeV diphoton invariant mass range using 80 fb$^{-1}$ of $pp$ collisions collected at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for low-mass diphoton resonances is performed using 80 fb$^{-1}$ of $pp$ collision data collected with the ATLAS detector at the Large Hadron Collider. Pairs of isolated photon candidates with high transverse momentum are selected, probing the diphoton invariant mass spectrum in the range 65 to 110 GeV. No significant excess with respect to the Standard Model expectation is found, and a limit at the 95% confidence level is set on narrow resonance fiducial cross-section times branching ratio ranging from 30 to 101 fb.