Photo-Mesons from Carbon

Photons from the Berkeley 322-Mev electron synchrotron have been used to produce mesons from a carbon target. These mesons have been observed with nuclear emulsions at angles of 45°, 90°, and 135° to the photon beam. The ratio of the number of ${\pi }^{-}$ to ${\pi }^{+}$ mesons produced is 1.29±0.22, 1.30±0.12, and 1.34±0.20, respectively, at each of the above angles. The energy spectra and the differential cross sections of $\pi$-mesons at each of these angles have been obtained. The total cross section for the production of $\pi$-mesons is 4.0±1.6×${10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$ per nucleus per "equivalent quantum." The number of "equivalent quanta," $Q$, is defined as the total energy in the beam divided by the maximum photon energy. The cross section for production of $\mu$-meson pairs at the target is estimated to be less than 2 percent of the cross section for $\pi$-meson production.