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

Abstract

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: $\mathrm{}\left(a\right)\mathrm{} p+p\to p+p+{\pi }^{+}+{\pi }^{-} 2.96\pm 0.12 \mathrm{mb},$ $\mathrm{}\left(b\right)\mathrm{} p+p\to p+p+{\pi }^{+}+{\pi }^{-}+{\pi }^0 1.76\pm 0.07 \mathrm{mb},$ $\mathrm{}\left(c\right)\mathrm{} p+p\to p+n+{\pi }^{+}+{\pi }^{+}+{\pi }^{-} 2.19\pm 0.09 \mathrm{mb}.$ 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 $\rho$ exchange in the reaction $p+p\to N^{*++}+N^{*0\mathrm{}}$. The formation of the $\eta$- and $\omega$-meson resonances is observed in reaction (b), but in none of the reactions studied is any significant $\rho$-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 $p{\pi }^{+}{\pi }^{+}$ ($I=\frac{5}{2}$) 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.