Strange-Particle Production inπ−pInteractions from1.5 to 4.2 BeVc. I. Three-and-More-Body Final States

We have investigated ${\pi }^{-}p$ interactions from $1.5 \mathrm{to} 4.2 \frac{\mathrm{BeV}}{c}$ in the Lawrence Radiation Laboratory's 72-in. hydrogen bubble chamber. This report describes the procedures for identifying and analyzing the reactions involving strange-particle production, and the results obtained on three- and more-body final states. The analysis is based on 890 000 photographs, on which 50 000 strange-particle events were found. Cross sections for the constrained final states are presented as a function of the beam momentum. The peripheral production of low-lying resonances is found to be the outstanding feature of the reactions. Dalitz plots and their projections are shown for the three-body final states. Production of $Y_0^{}{}_{}{}^{*}\mathrm{}\left(1405\right)\mathrm{}$, $Y_0^{}{}_{}{}^{*}\mathrm{}\left(1520\right)\mathrm{}$, $Y_0^{}{}_{}{}^{*}\mathrm{}\left(1815\right)\mathrm{}$, $Y_1^{}{}_{}{}^{*}\mathrm{}\left(1385\right)\mathrm{}$, $K^{*}\mathrm{}\left(890\right)\mathrm{}$, and $K^{*}\mathrm{}\left(1440\right)\mathrm{}$ is observed, as well as the $K\overline{K}$ decays of the $A_2$ and the $\phi$ meson. Cross sections and angular distributions for production and decay of these resonances are presented. The results concerning the $K^{*}\mathrm{}\left(890\right)\mathrm{}$ are compared with absorption-model predictions. Effective-mass distributions for particle pairs and triplets are given for the four-body final states. In these states the $D$ and the $E$ meson and simultaneous $Y^{*}{K}^{*}$ production are also seen. Evidence concerning the quantum numbers of the $A_2$, the $D$, the $E$, and the $K^{*}\mathrm{}\left(1440\right)\mathrm{}$ is discussed. The behavior of the $K\overline{K}$ system near threshold is examined. A small amount of $\Xi$ production is observed, and the ${\Xi }^{*}\mathrm{}\left(1530\right)\mathrm{}$ is also seen.