Measurement of theΣ−Polarization in the Reactionπ−+p→Σ−+K+

Abstract

The average polarization of the ${\Sigma }^{-}$ produced in the reaction ${\pi }^{-}+p\to {\Sigma }^{-}+K^{+}$ has been measured between center-of-mass angles 134° and 166° for an incident ${\pi }^{-}$ momentum of 1145 MeV/c. A polarized proton target was used, and the ${\Sigma }^{-}$ polarization was found by measuring the difference in the production rate of $K^{+}$ mesons for protons polarized along the production-plane normal and against it. Spark chambers were used to record the ${\pi }^{-}$ and $K^{+}$ trajectories, and the ${\pi }^{-}$ momentum was obtained from a magnetic spectrometer while the $K^{+}$ 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 ${\Sigma }^{-}$ polarization was found to be -0.36±0.46.