Production of Heavy Unstable Particles by 1.37-Bev Pions

Five additional events interpreted as the production of heavy unstable particles by 1.37-Bev pions have been observed in a hydrogen-filled diffusion cloud chamber. In each case the observations are most naturally interpreted as due to the associated production of a hyperon and K-meson. These and earlier observations can be made consistent with known hyperon and K-meson masses if the reaction π^-+p→Σ⁰+θ⁰ is assumed to be a possibility with an immediate γ-decay Σ⁰→Λ⁰+γ as suggested by Gell-Mann and Pais. The total cross section for production of heavy unstable particles is estimated to be about 0.9 millibarn. The five new events confirm the previous indications that the Λ⁰'s tend to be emitted backwards in the center-of-mass system of the initial collision and to decay in a plane at a small angle to that of the production plane. The orientations of Λ⁰'s from the wall also support these angular correlations.