Energy Spectrum of Charged Pions from 2.2-Bev Protons on Be

Nuclear emulsions have been exposed to the radiations produced by 2.2-Bev protons incident upon an internal beryllium target in the Brookhaven Cosmotron. Particles have been identified and their energies determined by grain counts and multiple scattering measurements. Approximately 100 pion tracks have been studied at each of three laboratory angles, 12°, 18°, and 36° with respect to the direction of the incident beam. Assuming a simple nucleon-nucleon interaction in the target, these data correspond to spectra near 30°, 50°, and 90° in the center-of-mass system of two nucleons. Over this 30° to 90° angular range, the portion of the spectrum near 100 Mev is roughly isotropic, while in the 200- to 300-Mev range it is strongly anisotropic. A comparison of these and other results with recent calculations based on the isobar model reveal certain basic inconsistencies. The observed angular distributions appear qualitatively to be more in agreement with those to be expected from the statistical theory modified to include the final-state particle interactions and the conservation of angular momentum.