SPIN OBSERVABLES AT THRESHOLD FOR THE REACTION PBARP-]LAMBDA-BAR-LAMBDA

The observables measured in two-body reactions, such as cross sections, polarizations, spin correlations, and the singlet fraction, take on simpler forms at threshold since only a few partial waves contribute. A study of these observables at the ppBAR --> LAMBDA-LAMBDABAR threshold is made in this paper. Our results are compared to the recent LEAR PS185 measurements, and several interesting angle-dependent features of the data are seen to originate from normal threshold behavior. Using general threshold properties, some recently proposed physics models of this process are strictly tested in this energy region. Several constraints on the transition amplitudes are deduced and excellent fits to the data are achieved using a simple scattering length approach. We find that S-wave amplitudes, S-P interference, a strong tensor interaction, and P-wave splitting all play appreciable roles in the reaction near threshold.