Properties of Heavy Unstable Particles Produced by 1.3-Bevπ−Mesons

Abstract

A propane bubble chamber has been exposed to a ${\pi }^{-}$ beam of 1.3-Bev kinetic energy. The reactions ${\pi }^{-}+p\to {\Sigma }^{-}+K^{+},$ ${\pi }^{-}+p\to {\Lambda }^0+{\theta }^0,$ ${\pi }^{-}+p\to {\Sigma }^0+{\theta }^0,$ can be experimentally distinguished from carbon events. Results based on the first 55 such events are presented. The center-of-mass production distribution of the ${\Sigma }^{-}$ is peaked forward, that of the ${\Lambda }^0$ backward. No large anisotropies in the angular correlation of production and decay were found, so that we have no evidence for spin in excess of ½ for any of the three particles: ${\Sigma }^{-}$, ${\Lambda }^0$, or ${\theta }^0$. A study of the relative abundance of single and double $V$ production indicates that both ${\Lambda }^0$ and ${\theta }^0$ have either long-lived "states" or neutral decay modes. A statistical analysis gives ${\overline{\alpha }}_{{\Lambda }^0}={{0.3}_{-0.12\mathrm{}}}^{+0.15\mathrm{}}$, ${\overline{\alpha }}_{{\theta }^0}={{0.3}_{-0.12\mathrm{}}}^{+0.19\mathrm{}}$, for the normal charged decay probabilities (${\Lambda }^0\to {\pi }^{-}+p$; ${\theta }^0\to {\pi }^{+}+{\pi }^{-}$) of the ${\Lambda }^0$ and ${\theta }^0$, respectively. One event was analyzed to obtain the energy released in ${\Sigma }^{-}$ decay. ${\Sigma }^{-}\to {\pi }^{-}+n+Q$; $Q=118\mathrm{}\pm 2.6$ Mev. The ${\Sigma }^{-}$ lifetime on the basis of 16 decays is (${1.4}_{-0.5\mathrm{}}^{+1.6\mathrm{}}$)×

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