Evidence for Heavy-Particle Production Processes at Energies above 2×1011eV

Cosmic-ray flux measurements in the energy region ${10}^{10}$-${10}^{14}$ eV obtained by calorimeters on the satellites Proton I and II have shown results that are at variance with previous data. While a single power law provides an approximate fit to the all-particle spectrum, the primary proton flux falls sharply at energies above ∼5×${10}^{11}$ eV, indicating that at high energies protons become progressively scarcer in the primary flux. The cross section for particle production by protons on carbon is found to rise by 20% in the interval between 2×${10}^{10}$ and ${10}^{12}$ eV. Assuming that, in the energy region of interest, (1) the real proton flux is given by a single power law, and (2) the nuclear composition remains constant, we show that the satellite flux measurements can be explained by an energy-loss mechanism in the calorimeter, the loss being a function of the energy per nucleon rather than the total energy. Furthermore, this "$X$" process has a cross section of the right magnitude to account for the $p$-carbon cross-section measurements. The $X$ process could be described in terms of particle production or dissociation of the primary protons.