The Production of Positive Mesons by Photons

Experimental results are presented on the production of positive mesons in hydrogen and carbon, as a function of meson angle and energy. The principal results are as follows: The angular distribution in the case of hydrogen is rather flat in the region 45°-135° in the laboratory system, slightly peaked near 90°. This demonstrates that the pion is not a scalar. The excitation function at 90° rises approximately linearly to a plateau which starts at photon energies of about 260 Mev. This rise is slower than expected on the basis of a phase space argument. The total cross section for 255-Mev photons in hydrogen is 1.9±0.3×${10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$. The cross sections in carbon are lower, per proton, by a factor of approximately three. With respect to hydrogen, the meson energy distribution is shifted to lower energies and the angular distribution is shifted to the backward angles.