REANALYSIS OF WEAK RADIATIVE HYPERON DECAYS IN COMBINED SYMMETRY AND VECTOR-DOMINANCE APPROACH

Following recent measurements of the XI-0 --> LAMBDA-gamma and XI-0 --> SIGMA-0-gamma decays we carry out a reanalysis of the combined symmetry and vector-dominance approach to weak radiative hyperon decays. The parity-conserving amplitudes are obtained from those of nonleptonic hyperon decays in two ways: (1) in the pole model and (2) by assuming that the parity-conserving part of the weak Hamiltonian H(w)PC transforms as lambda-7. Both are considered since, although the two frameworks are theoretically close, their numerical predictions are fairly different. Nonleptonic hyperon decays also fix two of three parameters needed to describe parity-violating amplitudes. The third parameter is then determined from fits to all the branching ratios and asymmetries of weak radiative hyperon decays measured so far. The fits strongly favor a substantial positive asymmetry-alpha for the XI- --> SIGMA--gamma decay (alpha approximately +0.2 to +0.6). The largest value (+0.6) is predicted by the best (and perfect: chi-2/N(DF) =7.9/7) fit obtained with H(w)PC approximately gamma-7 and photon-baryon coupling determined by experimental values of baryon magnetic moments.