Hyperon and Antihyperon Production inp¯−pCollisions at 7 BeV/c

Abstract

Production of hyperons and antihyperons in the interactions of 6.935 BeV/c antiprotons with protons has been studied. A total of 80 000 pictures taken with the Brookhaven National Laboratory 80-in. liquid-hydrogen bubble chamber have been analyzed for all possible final states involving the production of a hyperon and/or an antihyperon. The total cross section for events in this category is 1.3\ifmmode\pm\else\textpm\fi{}0.1 mb. Reactions leading to two-, three-, or four-body final states involving $\ensuremath{\Lambda}$ or $\ensuremath{\Sigma}$ hyperons (or their antiparticles) were produced highly peripherally. The angular distribution of the $\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}$ final state can be fitted to ${K}^{*}$ (888) exchange when the absorptive effect of competing channels is taken into account. Ratios among cross sections of various hyperon-antihyperon pair states agree with predictions from $S{U}_{3}$ symmetry, assuming a dominant $K$ or ${K}^{*}$ exchange and an $F$-type coupling. Charge ratios of events with ${\ensuremath{\Sigma}}^{\ifmmode\pm\else\textpm\fi{}}$ and ${{Y}_{1}}^{*\ifmmode\pm\else\textpm\fi{}}$ (1385) are also consistent with single-particle-exchange models. We have examined the mass spectra of all possible mass combinations of all possible final states. The ${{Y}_{1}}^{*}$ (1385) was by far the most prominent resonance produced, and production of ${{Y}_{0}}^{*}$ (1405) and ${{Y}_{0}}^{*}$ (1520) was also observed. Although the energy available in the production center-of-mass system is 3.86 BeV, there was no statistically significant evidence for the production of any new meson or baryon resonance. A thorough search has been made for ${\ensuremath{\Omega}}^{\ensuremath{-}}$ and ${\overline{\ensuremath{\Omega}}}^{+}$ particles, but no event was found to be consistent with their production and decay.