Elastic Scattering of 5-Bevπ−Mesons on Hydrogen

Abstract

The elastic scattering of 5-Bev negative pions on hydrogen has been observed in a large propane bubble chamber. We report below the results of this observation. It is shown that ≈(7±3)% of the events called elastic are probably background. The observed angular distribution is strongly peaked forward. This fact suggests that diffraction scattering is the dominant process at this energy. The theoretical analysis of the distribution is in terms of the optical model. It is shown that the proton acts like a partially opaque sphere of radius 1.04×${10}^{-13\mathrm{}}$ cm±5%. The total elastic cross section is found to be 5.6±0.5 mb. From the extrapolated value of $\frac{d\sigma \mathrm{}\left(0\right)\mathrm{}}{d\Omega }=29.8\mathrm{}$ mb/sr±10% in the center-of-mass system, a value of 29.1±2.9 mb was calculated for the total hydrogen cross section. The opacity of the sphere is thus 0.69±0.05.