Two-hundred thirteen events of the type ${\pi }^{-}+p\to {\pi }^{-}+{\pi }^{-}+{\pi }^{+}+p$ occurring in the Shutt 20-in. hydrogen bubble chamber at an incident-beam momentum of 7.0 BeV/c have been analyzed. The event separation has been performed utilizing kinematic fitting and ionization criteria. The contamination of the sample due to other final states is less than 10%. The cross section for this reaction has been measured to be 1.7±0.2 mb. The partial cross sections for the production of resonant final states have been measured with the results: $\sigma ({\pi }^{-}+p\to {\pi }^{-}+{\pi }^{-}+N^{*++})=0.55\mathrm{}\pm 0.11$ mb; $\sigma ({\pi }^{-}+p\to {\pi }^{-}+{\rho }^0+p)=0.38\mathrm{}\pm 0.10$ mb; and $\sigma ({\pi }^{-}+p\to N^{*0\mathrm{}}+{\rho }^0)=0.035\mathrm{}\pm 0.013$ mb. The $N^{*++}$ isobar mass and width were found to be 1216±14 MeV and 114±30 MeV, respectively. The ${\rho }^0$ parameters are $M^{*}=773\mathrm{}\pm 12$ MeV and $\Gamma ={{57}_{-15\mathrm{}}}^{+25\mathrm{}}$ MeV. ${\rho }^0$ production is peripheral and is dominated by final states with low ${\pi }^{-}{\rho }^0$ effective mass; limited statistics prevent us from resolving this enhancement into the $A_1$ and the $A_2$. Angular distributions in the ${\pi }^{-}{\rho }^0$ and the ${\rho }^0$ rest frames are presented as a function of the ${\pi }^{-}{\rho }^0$ mass. Conclusions drawn about the spin-parity of the $A_1$ and the $A_2$ from these distributions are highly model-dependent The model used indicates that the most likely spinparity assignments for the $A_2$ are, in order of likelihood, $2^{-}$, $1^{-}$, or $1^{+}$. If the $A_1$ is a resonance rather than a kinematic reflection, its most likely spin-parity assignments are $1^{+}$ or $2^{-}$.

• Received 7 March 1966

DOI:https://doi.org/10.1103/PhysRev.148.1282