Polarization measurement of the $\Sigma^+$ produced in the line-reversed reactions $\pi^+p \rightarrow K^+\Sigma^+$ and $K^-p \rightarrow \pi^-\Sigma^+$ at 7 and 11.6 GeV/c

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