p−pInteractions at 2 Bev. I. Single-Pion Production

3600 two-pronged events, obtained in $p-p$ interactions at 2 Bev in the BNL 20-in. hydrogen bubble chamber, have been analyzed. Cross sections have been measured for elastic scattering, for the two modes of single-pion production, $p+p\to p+n+{\pi }^{+}$, $p+p\to p+p+{\pi }^0$, and for strange-particle production. The branching ratio for the two one-pion production reactions is $\frac{\sigma \left(pn{\pi }^{+}\right)}{\sigma \left(pp{\pi }^0\right)}=4.17\mathrm{}\pm 0.25$. Momentum distributions and $Q$ values indicate that single-pion production proceeds almost entirely through the ($\frac{3}{2}, \frac{3}{2}$) resonant state. The data have been considered in terms of the extended isobar model and also a one-pion exchange model for production. The branching ratio and momentum distributions can be explained by including a small effect from the $I=\frac{1}{2}$ resonant state in addition to the dominant $I=\frac{3}{2}$ resonance. The c.m. angular distribution of the nucleons in single-pion production shows very marked backward-forward peaking indicating a one-pion exchange mechanism. Absolute differential cross sections as a function of laboratory kinetic energy have been calculated from Selleri's equation for the $\mathrm{pn}{\pi }^{+}$ reaction. There is good agreement with the data for low four-momentum transfers [$q^2<0.15\mathrm{}$ ${(\mathrm{B}\mathrm{e}\mathrm{v}/\mathit{c})}^2$], but for higher momentum transfers the theoretical cross sections are larger than the experimental cross sections.