Production and Decay of Cascade Hyperons

The production of cascade hyperons by $K^{-}$ incident on hydrogen has been studied at beam momenta of 1.7, 2.1, and 2.4-2.7 GeV/c. A sample of $3028{\Xi }^{-}$ and $934{\Xi }^0$ was obtained. Cross sections and polarization for ${\Xi }^{-}{K}^{+}$ and ${\Xi }^0{K}^0$ production are presented. The data are compatible with dominance by $I=0\mathrm{}$ baryon exchange in ${\Xi }^{-}{K}^{+}$ production, but also provide strong evidence for resonance formation in the $s$ channel compatible with ${Y_0}^{*}\mathrm{}\left(2100\right)\mathrm{}$. Copious production of ${\Xi }^{*}\mathrm{}\left(1530\right)\mathrm{}$ and $K^{*}\mathrm{}\left(890\right)\mathrm{}$ is observed in the three-and four-body final states. A broad $\Xi \pi$ enhancement is observed in the ${\Xi }^{-}{K}^{+}{\pi }^0$ and ${\Xi }^0{K}^{+}{\pi }^{-}$ final states at a mass near 1894 MeV/${\mathit{c}}^2$ and with a width of about 98 MeV/${\mathit{c}}^2$. This enhancement is identified with the ${\Xi }^{*}\mathrm{}\left(1930\right)\mathrm{}$ first observed by Badier et al. Lifetime measurements give ${\tau }_{{\Xi }^{-}}=(1.61\mathrm{}\pm 0.04)\times {10}^{-10\mathrm{}}$ sec and ${\tau }_{{\Xi }^0}=\left({{3.07}_{-0.20\mathrm{}}}^{+0.22\mathrm{}}\right)\times {10}^{-10\mathrm{}}$ sec. A decay-parameter analysis assuming spin ½ yields ${\alpha }_{{\Xi }^{-}}=-0.391\mathrm{}\pm 0.045$, ${\alpha }_{{\Xi }^0}=-0.43\mathrm{}\pm 0.09$,