Production of Strange Particles by 1.5-Bev π− Mesons in C, Fe, and Pb

The production of ${Y}^{0}$ (${\ensuremath{\Lambda}}^{0}, {\ensuremath{\Sigma}}^{0}$), ${\ensuremath{\theta}}^{0}$, ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ particles by 1.5-Bev ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons has been observed in a multiplate cloud chamber with one-half inch plates of C, Fe, and Pb. The fraction of the inelastic nuclear interactions which result in strange particle production remains approximately constant from C to Pb, with the following yields: ${Y}^{0}$, 1.7\ifmmode\pm\else\textpm\fi{}0.4%; ${\ensuremath{\theta}}^{0}$, 1.4\ifmmode\pm\else\textpm\fi{}0.5%; ${\ensuremath{\Sigma}}^{\ensuremath{-}}$, 0.2\ifmmode\pm\else\textpm\fi{}0.1%. The production angular and momentum distributions are given, along with the distributions obtained from Monte Carlo calculations which do not include secondary interactions of the strange particles.The yields of hyperons and ${\ensuremath{\theta}}^{0}'\mathrm{s}$ are close to those expected on the basis of the known cross sections in elementary $\ensuremath{\pi}\ensuremath{-}p$ collisions. However, the $\frac{{\ensuremath{\Sigma}}^{\ensuremath{-}}}{{Y}^{0}}$ ratio is observed to be much less than expected, indicating at least geometric cross section for ${\ensuremath{\Sigma}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{Y}^{0}+n$.The following lifetimes were obtained: ${\ensuremath{\Lambda}}^{0}$, (${2.72}_{\ensuremath{-}0.27}^{+0.29}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec; ${{\ensuremath{\theta}}_{1}}^{0}$, (${1.09}_{\ensuremath{-}0.15}^{+0.18}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec. No statistically significant ${\ensuremath{\Lambda}}^{0}$ decay asymmetries (up-down, forward-backward, decay proton scattering) were found. Four likely and two possible examples of ${{\ensuremath{\theta}}_{2}}^{0}$ interactions were observed, in good agreement with the number expected if the interaction cross section were geometric.