π−−pInteractions at 683 MeV/c

Interactions of 683-MeV/c negative pions with protons were investigated using the BNL 14-in. hydrogen bubble chamber in a 17-kG field. Two thousand elastic scatterings were analyzed, yielding a cross section of 18.9±1.0 mb. No evidence for powers of $cos\theta$ higher than the second was observed in the elastic angular distribution. The angular distribution obtained was $\frac{d\sigma }{d\omega }=(0.384\mathrm{}\pm 0.026)+(1.70\pm 0.06)cos\theta +(3.36\mathrm{}\pm 0.11){cos}^2\theta$ mb/sr. The single-pion production reactions ${\pi }^{-}+p\to {\pi }^{-}+{\pi }^0+p$ and ${\pi }^{-}+p\to {\pi }^{-}+{\pi }^{+}+n$ were studied in detail. A total of 441 ${\pi }^0$ productions and 833 ${\pi }^{+}$ productions were analyzed giving cross sections of 3.99±0.50 and 7.50±0.80 mb, respectively. The differential distributions for these inelastic processes are presented and compared with the predictions of the model of Olsson and Yodh. The distribution of events on the Dalitz plots for ${\pi }^0$ production is accounted for by the model. However, for the ${\pi }^{+}$ reaction, the model (so far developed) does not describe adequately the distribution of events on the Dalitz plot. In particular, the model fails to account for the enhancement at high (${\pi }^{+}{\pi }^{-}$) effective masses in $\pi \pi$ mass distribution. The center-of-mass angular distributions for ${\pi }^0$ and ${\pi }^{+}$ production reactions are presented and compared with the model.