Scattering of 151- and 188-Mev Positive Pions by Protons

Abstract

A beam of ∼200-Mev ${\pi }^{+}$ mesons was defined inside the vacuum chamber of the Nevis Cyclotron. Nuclear emulsions were exposed to a flux of about ${10}^4$ mesons/${\mathrm{cm}}^2$. The plates were scanned for pion-hydrogen scatterings and 103 such events were observed in two interaction energies, 151±7 Mev and 188±8 Mev. We obtain total cross sections of 152±31 and 159±34×${10}^{-27\mathrm{}}$ ${\mathrm{cm}}^2$, respectively. The data suggest that the angular distribution changes from backwards peaked to almost symmetric over this energy interval. Our observations are not in agreement with the hypothesis of a $P_{\frac{3}{2}}$-wave resonance in this energy region. The best fit to the combined results includes a $D$-wave contribution of -5.4°, although satisfactory agreement may be obtained with only $S$ and $P$ waves.