MEASUREMENT OF THE SIGMA- POLARIZATION IN THE REACTION pi- + p --> SIGMA- + K+

The average polarization of the {Sigma}{sup -} produced in the reaction {pi}{sup -} + p {yields} {Sigma}{sup -} + K{sup +} has been measured between center-of-mass angles 134{sup o} and 166{sup o} for an incident {pi}{sup -} momentum of 1145 MeV/c. A polarized proton target was used, and the {Sigma}{sup -} polarization was found by measuring the difference in the production-rate of K{sup +} mesons for protons polarized along the production-plane normal and against it. Spark chambers were used to record the {pi}{sup -} and K{sup +} trajectories, and the {pi}{sup -} momentum was obtained from a magnetic spectrometer while the K{sup +} momentum was obtained from a range telescope. Each event was kinematically reconstructed in a one constraint fit to help eliminate events produced from protons bound in heavy nuclei of the target. The {Sigma}{sup -} polarization was found to be -0.36 {+-} 0.46.