Multiple Pion Production in Interactions of Positive Pions with Protons Near 1 BeV

Abstract

We report results of a study of multiple pion production in the reactions ${\ensuremath{\pi}}^{+}p\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{+}p\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ at pion kinetic energies 910 MeV, 1090 MeV, and 1260 MeV. Double pion production is dominated by production of the ${N}^{*}(\frac{3}{2}, \frac{3}{2})$ nucleon isobar and no other resonant states among the outgoing particles are identified. Triple pion production proceeds almost entirely by formation of the $\ensuremath{\eta}$ meson (mass 549 MeV) which subsequently decays into (${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$). The isotopic spin of the $\ensuremath{\eta}$ is confirmed to be $I=0$ and the spin $J$, parity $P$, and $G$-parity $G$ are confirmed to be most likely ${J}^{\mathrm{PG}}={0}^{\ensuremath{-}+}$. The relative decay rate $\frac{(\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma})}{(\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0})}$ is found to be 0.14\ifmmode\pm\else\textpm\fi{}0.08, and the decay ratio $\frac{(\ensuremath{\eta}\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{0})}{(\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0})}$ is found to be 2\ifmmode\pm\else\textpm\fi{}1. No $\ensuremath{\eta}'\mathrm{s}$ were observed at 910 MeV. At 1090 MeV and 1260 MeV, the production angular distributions of the $\ensuremath{\eta}$ are roughly isotropic. $\ensuremath{\eta}$ production appears to be associated with the production of the ${N}^{*}(\frac{3}{2}, \frac{3}{2})$ isobar, in the ($p, {\ensuremath{\pi}}^{+}$) system.