M.S.

Approximately 6,000 two prong events from proton-proton interactions at 2.8 Bev/c have been analyzed in order to study single π° production. The center-of-mass momentum distributions of the final state protons and pions have been found to be in generally good agreement with the theoretical predictions based upon the Isobar model. The distribution of the square of the four-momentum transfer to the target proton shows a very strong tendency towards small momentum transfer, i.e. glancing collisions. In addition the center-of-mass angular distribution of protons shows a very strong forward-backward peaking, thus indicating the presence of high partial waves in the interaction process. In general, all data is in good qualitative agreement with the One Pion Exchange (OPE) model. The Treiman-Yang test has been applied to test the validity of OPE. The nearly isotropic distribution of the Treiman-Yang angle is indicative of the fact that one pion exchange is by far the predominant interaction mechanism. The Dalitz plot and the pπ° effective mass distribution both clearly show the formation of the isobar N*_3/2 (1236) and both also show some indication of the formation of Ni*_1/2 (1518), but this latter isobar does not show up so strongly as the former because the cross-section for the , formation of Ni*_1/2 is quite small. Finally, the angular distribution of the pion in the isobar rest system relative to the direction of the beam proton as seen in the isobar system does not show the expected 1 + 3 cos² θ dependence. The observed dependence is approximately 1 - 0.4 cos θ + 0.6 cos² θ. It is believed that the discrepancy may be accounted for by interference effects between the two isobars. / M.S.