Measurement of the branching ratio for the Xi ---> Sigma - gamma radiative decay.

We have measured the branching ratio for the hyperon radiative decay XI- --> SIGMA- gamma from a sample of 211 +/- 33 events obtained in the polarized 375 GeV/c charged hyperon beam at Fermilab. We find B(XI- --> SIGMA- gamma/XI- --> LAMBDA0pi-) = (1.22 +/- 0.23 +/- 0.06) X 10(-4) where the quoted errors are statistical and systematic, respectively. We have also obtained an indication that the sign of the asymmetry parameter of this decay is positive.