π−pBackward Elastic and Inelastic Scattering at 2.15 GeV/c

Abstract

We have measured differential cross sections for the reactions ${\pi }^{-}p\to {\pi }^{-}p$ and ${\pi }^{-}p\to {\pi }^{\pm }{N}^{*\mp }\mathrm{}\left(1236\right)\mathrm{}$ at an incident pion momentum of 2.15 GeV/c and for center-of-mass scattering angles in the range ${cos\theta }^{*}=-0.999\mathrm{} \mathrm{to} -0.950\mathrm{}$. The elastic differential cross section has a sharp dip in the backward direction, dropping from ∼70 μb/sr at ${cos\theta }^{*}=-0.95\mathrm{} \mathrm{to} \sim 4$ μb/sr at ${cos\theta }^{*}=-1\mathrm{}$; the $N^{*-}\mathrm{}\left(1236\right)\mathrm{}$ differential cross section is, within our errors, consistent with the same size and shape as that for elastic scattering; the average differential cross section for $N^{*+}\mathrm{}\left(1236\right)\mathrm{}$ in our angular region is less than 18 μb/sr with 97% confidence.