Charge Exchange Scattering of 128-Mev Negative Pions on Hydrogen

The charge exchange scattering of negative pions by liquid hydrogen has been measured at 128±2 Mev bombarding energy. A lead-glass Čerenkov counter was used to measure the energy spectrum of the gamma rays emitted in the decay of the neutral pions. The gamma rays were detected at four angles relative to the incident beam: 45°, 80°, 116°, and 135°. If the charge exchange scattering cross section is expanded as a sum of Legendre polynomials which are functions of the ${\pi }^0$ scattering angle in the center-of-mass system, we find that $\frac{d\sigma }{d\Omega }({\pi }^{-}, {\pi }^0)=(1.00\mathrm{}\pm 0.04)\left[\right(2.04\pm 0.06)+(-1.61\pm 0.13)P_1+(1.43\mathrm{}\pm 0.24\left)P_2\right],$ when only $s$ and $p$ waves are considered. The confidence level for the least-squares fit used to determine the coefficients inside the square brackets is 65%. The integrated cross section is ${\sigma }_{\mathrm{tot}}({\pi }^{-}, {\pi }^0)=25.6\mathrm{}\pm 1.3$ mb, which is in good agreement with other work.