π − p interactions at 4.0 GeV/c

A bubble chamberinvestigation of π−p interactions has been carried out at a momentum of 4 GeV/c. Analysis is limited to 2128 events with four charged secondaries. Cross-sections for the different reactions includingN*++, ρ0 and ω production are given. Reactions are discussed in the light of the one- pion-exchange model. TheN*, ρ and ω resonances are found to be produced in peripheral interactions. Possible existence of a dipion resonance at 500 MeV shows up, however no evidence for the production in four-prong events of ABC, ζ or f0 resonances could be obtained while the production ofη’s proved to be greatly suppressed due to phase-space limitations. A tentative figure for aT=2 (nonresonant) pion-pionscattering cross-section is given. C.m.s. angular distributions are characterized by a backward going nucleon and one of the pions(in most reactions a negative one) going forward, the rest of the pionsbeing distributed more or less isotropically. With increasing multiplicity the angular distributions become more isotropic and the resonances are smeared out. This fact may be explained by an increasing importance of final-state interactions and by a less peripheral type of production mechanism.