Experiments on Antiprotons: Cross Sections of Complex Nuclei

Experiments are described that have been designed to measure separately annihilation and reaction cross sections for antiprotons of approximately 450 Mev on oxygen, copper, silver, and lead. A new and more luminous spectrograph has been built for this experiment. The antiproton cross sections are compared with total proton cross sections, and are found to be larger by a factor varying from 1.74 for oxygen to 1.39 for silver. Calculations based on the optical model give a reasonable connection between these cross sections and the p̄-p and p̄-n cross sections. Finally, the information available on antiproton production cross sections is collected. There are indications that a free nucleon is several times as effective as a bound one for producing antiprotons.