Simulation study on the effects of diffractive collisions on the prediction of the observables in ultra-high-energy cosmic-ray experiments

The mass composition of ultra-high-energy cosmic rays is important for understanding their origin. Owing to our limited knowledge of the hadronic interaction, the interpretations of the mass composition from observations have several open problems, such as the inconsistent interpretations of $\langle X_{\mathrm{max}}\rangle $ and $\langle X_{\mathrm{max}}^{\mu}\rangle $ and the large difference between the predictions by the hadronic interaction models. Diffractive collision is one of the proposed sources of the uncertainty. In this paper, we discuss the effect of the detailed characteristics of diffractive collisions on the observables of ultra-high-energy cosmic-ray experiments by focusing on three detailed characteristics. These are the cross-sectional fractions of different collision types, diffractive-mass spectrum, and diffractive-mass-dependent particle productions. We demonstrated that the current level of the uncertainty in the cross-sectional fraction can affect 8.9$\mathrm{g/cm^2}$ of $\langle X_{\mathrm{max}}\rangle $ and 9.4$\mathrm{g/cm^2}$ of $\langle X_{\mathrm{max}}^{\mu}\rangle $, whereas the other details of the diffractive collisions exhibit relatively minor effects.