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 ${\pi }^{+}p\to p{\pi }^{+}{\pi }^{+}{\pi }^{-}$ and ${\pi }^{+}p\to p{\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ 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 $\eta$ meson (mass 549 MeV) which subsequently decays into (${\pi }^{+}{\pi }^{-}{\pi }^0$). The isotopic spin of the $\eta$ is confirmed to be $I=0\mathrm{}$ and the spin $J$, parity $P$, and $G$-parity $G$ are confirmed to be most likely $J^{\mathrm{PG}}=0^{-+}$. The relative decay rate $\frac{(\eta \to {\pi }^{+}{\pi }^{-}\gamma )}{(\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0)}$ is found to be 0.14±0.08, and the decay ratio $\frac{(\eta \to 3{\pi }^0)}{(\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0)}$ is found to be 2±1. No $\eta \text{'}\mathrm{s}$ were observed at 910 MeV. At 1090 MeV and 1260 MeV, the production angular distributions of the $\eta$ are roughly isotropic. $\eta$ production appears to be associated with the production of the $N^{*}(\frac{3}{2}, \frac{3}{2})$ isobar, in the ($p, {\pi }^{+}$) system.