Breakdown of Feynman scaling in high-energy cosmic-ray interactions

Abstract

Extensive Monte Carlo calculation on $\ensuremath{\gamma}$-ray families was carried out under appropriate model parameters which are currently used in high-energy cosmic-ray phenomenology. Characteristics of $\ensuremath{\gamma}$-ray families are systematically investigated by the comparison of calculated results with experimental data obtained at mountain altitudes. The discussion is devoted mainly to examining the validity of Feynman scaling in the fragmentation region of multiplemeson production. It is concluded that the experimental data cannot be reproduced under the assumption of the scaling law if primary cosmic rays are dominated by protons. Other possibilities on primary composition and increase of interaction cross section are also examined. These assumptions are consistent with experimental data only when we introduce intense dominance of heavy primaries in the high-energy region and very strong increase of the interaction cross section (say $\ensuremath{\sigma}\ensuremath{\propto}{{E}_{0}}^{0.06}$) simultaneously. Otherwise, the breakdown of Feynman scaling in the fragmentation region and the existence of azimuthal asymmetry in production mechanism are strongly suggested by high-energy cosmic-ray interactions (${E}_{0}\ensuremath{\gtrsim}{10}^{15}$ eV).