Production of Strange Particles byπ−−pInteractions near Threshold

Observations have been made, in a liquid hydrogen bubble chamber, of the production and decay of strange particles produced by the interaction of 960-Mev ${\pi }^{-}$ mesons with protons. The total strange particle production cross section was measured to be 1.02±0.20 millibarns. The cross section is 0.58±0.12 millibarn for ${\Lambda }^0-{\theta }^0$ production, 0.35±0.09 millibarn for ${\Sigma }^0-K^{+}$ production, and is 0.09±0.04 millibarn for ${\Sigma }^{-}-K^{+}$ particles. Production angular distribution was peaked somewhat backwards for ${\Sigma }^0$ and ${\Lambda }^0$ hyperons. These cross sections, together with other data, are interpreted as indicating the existence of a very strong interaction for the production of strange particles which extends over a small radius. The decay products of the ${\Lambda }^0$ hyperons from ${\Lambda }^0-{\theta }^0$ production were preferentially aligned with the incoming beam, a result suggesting a spin of $\frac{3}{2}$ for the ${\Lambda }^0$. Decay distributions for ${\Lambda }^0$ particles resulting from ${\Sigma }^0$ decay, and for ${\theta }^0$ mesons, were consistent with isotropy.