Large-Angle Pion-Proton Elastic Scattering at High Energies

Differential cross sections for elastic ${\pi }^{\pm }-p$ scattering have been measured at lab momenta of 8 and 12 GeV/c in a momentum-transfer region corresponding to $1.2\le -t\le 6$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. Also, differential cross sections near 180° were measured for 4 and 8 GeV/c pions. At momentum transfers greater than $-t=2\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, the $\pi -p$ cross sections drop much faster with increasing angle than the corresponding $p-p$ cross sections. Also, in the region $-t\simeq 1.3$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, there is structure in the $\pi -p$ angular distribution but not in the $p-p$ angular distribution. At $-t\simeq 3$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, the drop in cross section appears to stop and from then on the angular distribution is consistent with isotropy. But in the angular region 170° to 180°, the cross sections have become much larger, and sharp backward peaks are observed. Information is given on the energy and charge dependences and widths of these backward peaks.