Measurement of contributions of diffractive processes to forward photon spectra in pp collisions at $\sqrt{s}$ = 13 TeV

This note presents a study of the contribution of proton diffractive dissociation to production of forward photons in pp collisions at $\sqrt{s}$ = 13 TeV with data recorded by the ATLAS and LHCf experiments in a joint effort. The results are based on data collected in 2015 with a corresponding integrated luminosity of 0.191 nb$^{-1}$. The data analysis is based on photon reconstruction in the LHCf-Arm1 detector, as well as on the inner tracking system of the ATLAS detector, which is used to identify diffractive events. In particular, the energy spectrum of photons in the pseudorapidity range of 8.81<$\eta$<8.99 or $\eta$>10.94 is measured for events with no reconstructed charged-particle tracks with $p_T$>100 MeV and |$\eta$|<2.5. The results are compared to predictions from several hadronic interaction models.