Search for new resonances in the diphoton final state in the mass range between 70 and 110 GeV in pp collisions at $\sqrt{s}=$ 8 and 13 TeV

The results of a search for a new resonance decaying into two photons are presented for a diphoton invariant mass in the range between 70 and 110 GeV. The analysis uses the entire dataset collected by the CMS experiment in proton-proton collisions during the 2012 and 2016 LHC running periods. The data samples correspond to integrated luminosities of $19.7~\mathrm{fb}^{-1}$ at $\sqrt{s}=8~\mathrm{TeV}$ and $35.9~\mathrm{fb}^{-1}$ at $\sqrt{s}=13~\mathrm{TeV}$. The expected and observed $95\%$ confidence level upper limits on the product of the cross section times branching ratio into two photons are presented. No significant excess with respect to the expected limits is observed. The observed upper limit for the 2012 (2016) dataset ranges from approximately 133 (161) fb at the mass hypothesis of 91.1 (89.9) GeV to 31 (26) fb at a mass of 102.8 (103.0) GeV. The statistical combination of the results from the analysis of the two datasets in the mass range between 80 and 110 GeV yields a minimum (maximum) observed upper limit on the production cross section times branching ratio normalized to the Standard Model-like expectation of approximately 0.17 (1.15) corresponding to a mass hypothesis of 103.0 (90.0) GeV.