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

A beam of \ensuremath{\sim}200-Mev ${\ensuremath{\pi}}^{+}$ 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\ifmmode\pm\else\textpm\fi{}7 Mev and 188\ifmmode\pm\else\textpm\fi{}8 Mev. We obtain total cross sections of 152\ifmmode\pm\else\textpm\fi{}31 and 159\ifmmode\pm\else\textpm\fi{}34\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}27}$ ${\mathrm{cm}}^{2}$, 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\ifmmode^\circ\else\textdegree\fi{}, although satisfactory agreement may be obtained with only $S$ and $P$ waves.