Pion-Proton Total Cross Sections from 0.45 to 1.9 Bev

Abstract

Measurements of the pion-proton total cross section over a range of kinetic energies from 0.45 to 1.9 Bev are described. Positive pions were distinguished from protons of the same momentum by a time-of-flight technique. A liquid hydrogen absorber was used for most of the measurements. Muons, the principal beam contamination, were approximately 10% of the pions.A pronounced maximum for $\ensuremath{\sigma}({\ensuremath{\pi}}^{\ensuremath{-}}, p)$ near 0.9 Bev, which had been noted in our preliminary measurements, is confirmed by data presented here. If this maximum is to be interpreted as a resonance in a single state of angular momentum, the analysis shows that, after subtracting a term which can reasonably be attributed to nonresonant states, the total angular momentum could be as low as $\frac{5}{2}$ without serious disagreement with experimental data. The possibility of explaining this maximum with a resonant pion-pion interaction as conjectured by Dyson and Takeda is discussed. The measurements of $\ensuremath{\sigma}({\ensuremath{\pi}}^{+}, p)$ also give evidence for the existence of a maximum of relatively smaller amplitude at 1.35 Bev.The differential cross section in the forward direction for elastic and charge-exchange scattering of pions by protons have been obtained by making use of the dispersion relations.