π+pInteractions at 900 MeV

We report the results of the investigation of 18 500 frames of ${\pi }^{+}p$ interactions in the Brookhaven 20-in. bubble chamber at an incident energy of 900 MeV. It is found that single-pion production proceeds almost entirely through formation of the ${N_{33}}^{*}$ isobar. The production mechanism of the ${N_{33}}^{*}$ is analyzed in terms of its spin density matrix. Comparison is made with Stodolsky and Sakurai's $\rho$-exchange model and with the absorptive peripheral model.