Multiple Meson Production by Photons in Hydrogen

The analysis of 235 events of double meson production by photons with energy up to 1.1 Bev (reaction $\gamma +p\to p+{\pi }^{+}+{\pi }^{-}$) observed in a ${\mathrm{H}}_2$ diffusion cloud chamber has produced the following results. The cross section rises rapidly at about 500 Mev to a value of approximately 70 μb. The angular, momentum, and $Q$ distributions of the reaction products cannot be satisfactorily accounted for either by a pure statistical model, or by a pure isobaric state model, or by a model assuming interaction of the incoming photon with the meson cloud of the proton, leading to $\pi -\pi$ interaction. The observation of 14 cases of the reactions $\gamma +p\to p+{\pi }^{+}+{\pi }^{-}+{\pi }^0$ and $\gamma +p\to n+{\pi }^{+}+{\pi }^{+}+{\pi }^{-}$ suggests that the combined cross section for these reactions is about 10 μb between 700 and 1000 Mev.