A Bubble-Chamber Study Of Proton-Proton Collisions At 4 Gev/C .2. Multiple Pion Production

About 50 000 pictures were taken in the 81 cm Saclay Hydrogen Bubble Chamber exposed at the CERN Proton-Synchrotron to a separated beam of 4 GeV/c incident momentum protons. Cross-sections for the various channels for multiple pion production are reported, as well as production cross-sections for baryon and boson resonances, taking into account the peripheral behaviour of the interaction in the evaluation of the background. All the channels appear to be dominated by theN1236* isobar production, while the presence of higher isobars does not seem to affect appreciably the general features of the different reactions. The only clear evidence among the boson resonances is for η (ση = (0.04 ± 0.02) mb) and ω (σω = (0.08 ± 0.03) mb). There is no strong evidence for theI=5/2 isobar around 1.58 GeV/c2. Finally an analysis of reactions producing more than one neutral particle has been tried, allowing an estimate of the mean multiplicitics for both charged and uncharged pions.