Pion-Proton Charge-Exchange Scattering from 500 to 1300 MeV

Differential cross sections for the reaction ${\pi }^{-}p\to {\pi }^{0}n$ were measured at nine incident-pion kinetic energies in the interval from 500 to 1300 MeV. The negative pion beam from the bevatron was focused on a liquidhydrogen target completely surrounded by a cubic array of six steel-plate spark chambers. The spark chambers were triggered on events with neutral final states. Charge-exchange events were identified from the one-shower and two-shower events in the spark-chamber pictures. By the Monte Carlo technique, the ${\pi }^0$ distributions were calculated from the bisector distributions of the two-shower ${\pi }^0$ events together with the observed $\gamma$-ray distributions of the one-shower ${\pi }^0$ events. These ${\pi }^0$ distributions were fitted with both Legendre-polynomial expansions and power-series expansions by the method of least squares. The extrapolated forward differential cross sections are in good agreement with the dispersion calculations. The Legendre coefficients for the differential cross sections in isospin state $T=\frac{1}{2}$ were obtained by combining our results with available data on ${\pi }^{\pm }p$ elastic scattering. In the light of existing phase-shift solutions, the behavior of these coefficients is discussed. The $D_5{F}_5$ interference term that peaks near 900 MeV is verified to be in isospin state $T=\frac{1}{2}$ only. We report here also the total neutral cross sections and the cross sections for the production of neutral multipion final states $2{\pi }^{0}n$ and $3{\pi }^{0}n$. The $4\pi$ solid angle and the calibrated energy response of the spark chambers contribute to the accuracy of the results.