Polarization Measurement of the Σ + Produced in the Line-Reversed Reactions π + p-->K + Σ + and K - p-->π - Σ + at 7 and 11.6 GeV/c

The polarization of the ${\ensuremath{\Sigma}}^{+}$ has been measured for the line-reversed reactions ${\ensuremath{\pi}}^{+}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{+}$ and ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\Sigma}}^{+}$ at 7 and 11.6 GeV/c using the SLAC Hybrid Facility. Since the ${\ensuremath{\Sigma}}^{+}$ decay is observed in the bubble chamber, the trigger of the flash lamps on a fast ${K}^{+}({\ensuremath{\pi}}^{\ensuremath{-}})$ did not bias the polarization measurements. We find that the ${\ensuremath{\Sigma}}^{+}$ polarizations from the two reactions have opposite signs but similar magnitudes and are in much better agreement with the predictions of weak exchange degeneracy than previous lower-energy comparisons.