Abundance of primary protons at(13)×1015 ev inferred from a simulation of extensive air showers with ray families

A Monte Carlo simulation of extensive air showers (EASs) was done under a particle-interaction model and was compared with the EASs accompanied by -ray and hadronic families with total energy JE,H greater than 10 TeV obtained in the Mt. Norikura experiment (2780 m above sea level). The strong correlation between the shower size Ne of EASs with family and the primary energy, E0, was obtained from the simulation as E0/Ne=(2.0-0.7+2.7) GeV with 95% width. The flux of the EASs with family is sensitive to the chemical composition, especially to the fraction of protons in the primary cosmic-ray particles. The fraction of protons is inferred to be (206)% and (239)%, with one standard deviation (1), at energy (1.4-0.5+1.9)×1015 eV and (2.8-1.0+3.8)×1015 eV with 95% confidence interval, respectively, under the assumption of increasing cross section p-airE0.055 and approximate Feynman scaling in the fragmentation region. These values are in agreement with the values obtained from other mountain emulsion-chamber experiments within 2. The proton fraction thus obtained, around 20%, is much less than the normal abundance (40%) expected from direct observations at lower energies around 1012 eV. 1989 The American Physical Society.