High-Energy Cross Sections. II. Nucleon-Nucleon Cross Section at Cosmic-Ray Energies

Abstract

Cosmic-ray measurements are capable of yielding reliable results for the cross section of a nucleus for proton or neutron collisions involving a not too small energy transfer. This cross section should therefore be less than, or at most equal to, the true nonelastic cross section (reaction cross section). Results of recent cosmic-ray work are assembled and compared with the reaction cross sections measured at 1.4 Bev with the Brookhaven Cosmotron; it is found that the cosmic-ray cross sections are significantly larger, even for Pb. Assuming a nonuniform distribution of the density of nuclear matter, one can explain this surprising effect as the result of an increase in the elementary nucleon-nucleon cross section with energy. It is shown that the elementary cross section (the average of ${\sigma }_{\mathrm{pp}}$ and ${\sigma }_{\mathrm{np}}$) must be (${120}_{-20\mathrm{}}^{+30\mathrm{}}$)×${10}^{-27\mathrm{}}$ ${\mathrm{cm}}^2$ in the neighborhood of 30 Bev.