Meson Production inn−pCollisions at Cosmotron Energies

Abstract

154 analyzable three-prong events were observed in collisions between Cosmotron-produced neutrons, with energies up to 2.2 Bev, and protons in a hydrogen-filled diffusion cloud chamber. These events were classified as a result of the reactions $n+p\to p+p+{\pi }^{-}$, $p+p+{\pi }^{-}+{\pi }^0$, and $p+n+{\pi }^{+}+{\pi }^{-}$ with frequencies in the ratio (0.8±0.3): (1±0.35): (3.2±0.7), respectively. The observed ratio of the probability for double meson production to that for single meson production is more than 20 times higher than the ratio predicted from Fermi's statistical model. No triple meson production is observed, in agreement with the statistical model. The momentum distributions of the observed mesons are also in rough agreement with the theory. In the center-of-mass system, in the reaction $n+p+{\pi }^{+}+{\pi }^{-}$, protons and ${\pi }^{+}$ show a tendency to be emitted backward, while neutrons and ${\pi }^{-}$ tend towards forward emission. However, the data suggest that protons and ${\pi }^{+}$, and also neutrons and ${\pi }^{-}$, tend to be emitted more frequently in opposite directions than protons and ${\pi }^{-}$ or neutrons and ${\pi }^{+}$. All of these results may be qualitatively in agreement with a meson production model where each nucleon is excited separately to an intermediate, possibly resonant, state which subsequently decays by emission of a meson.