Photoproduction of Positive Pions in Hydrogen-Counter Telescope Method

The excitation functions for positive pion production from hydrogen have been obtained in the energy region from 230 Mev to 450 Mev and at laboratory pion angles of 24°, 38°, 53°, 73°, 93°, 115°, 140°, and 160°. The pions are detected and identified by measuring their range and ionization in a scintillation counter telescope. The above data are analyzed to give the angular distributions in the center-of-momentum system, and a least-squares analysis made to determine coefficients in $\sigma \left(\theta \right)=A+Bcos\theta +C{cos}^2\theta$. The total cross section shows a peak at 300 Mev of magnitude 2.20×${10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$. The coefficient $B$ passes through a maximum negative value at 250 Mev and then passes through zero at 325 Mev and remains positive up to the highest energy measured.