Isobar Production Mechanisms in Proton-Proton Collisions at 5 GeV/c

Approximately 7500 four-prong proton-proton collisions at 5 GeV/c have been studied using the BNL 80-in. hydrogen bubble chamber. The three principal reactions studied with their cross sections are: (a) p+p→p+p+π⁺+π^- 2.96±0.12 mb, (b) p+p→p+p+π⁺+π^-+π⁰ 1.76±0.07 mb, (c) p+p→p+n+π⁺+π⁺+π^- 2.19±0.09 mb. In each reaction both single and double N* production occurs and the decay angular distributions and density matrix elements have been calculated whenever possible. These parameters indicate that pseudo-scalar (pion) exchange appears to be dominant at low values of momentum transfer and that at higher momentum transfer absorptive effects become important. We find no evidence for ρ exchange in the reaction p+p→N*+++N*0. The formation of the η- and ω-meson resonances is observed in reaction (b), but in none of the reactions studied is any significant ρ-meson production found to occur. In reaction (c) we find a deviation from phase space in the region of the 1580-MeV mass bump in the pπ⁺π⁺ (I=5/2) system which was observed by Alexander et al., but we ascribe this departure from phase space at our energy as being principally due to N*++ and N^*- formation in this channel.