Weak Radiative Decays of Hyperons and Charmed Baryons in SU(4) and SU(8) (original) (raw)
We study the weak radiative decays of uncharmed and charmed baryons in the SU(4) and SU(S) symmetry framework. \Ve find that the GIM model of weak interactions gives unsatisfactory results for the weak radiative decays of uncharmed baryons, at SU(4) leveL An admixture of 15-dimensional representation of SU(4) in the GIM weak Hamiltonian is indicated. We propose measurement of the decay z->.s-r in order to elucidate the structure of the weak Hamiltonian. § 1. Introduction Weak radiative decays of hyperons have been discussed by several authors 11 in the domain of SU(3) symmetry. The available experimental information about these decays is meagre. Definite numbers have been reported for the process 2+-'>Pt only. We have 21 T(2~-'>Pt)_ = (1.43±0.26) X 10-3 r (2+->all) and the asymmetry parameter a for this decay is (-1.03:':UD. Even this small information about the weak radiative decays has been a source of considerable difficulty for the weak interaction phenomenology. In the current ~ current model of weak interactions, if one assumes the same behaviour under C (charge conjugation) for the parity violating (pv) and parity conserving (pc) parts of the weak Hamiltonian the asymmetry parameter for 2+ decay turns out to be zero. 11 A small negative value for a can be obtained in pole models by making certain assumptions about the intermediate states. 31 " 11 But a large value of a (2+->Pr) remains unexplained. A simple way out is to assume that the pv and pc parts of the weak Hamiltonian have opposite behaviour under C. This means that at the SU(3) level one assumes the pv Hamiltonian to transform as }., component of the octet and the pc Hamiltonian to transform as J.6 • This choice for the weak Hamiltonian has already been proposed in the context of quark-density model, 51 and has the attractive feature that K,->27r is not zero in the SU(3) limit. This SU(3) structure for the weak Hamiltonian is also obtained in recent models with right-handed currents. 61 With this assumption, both pv and pc parts of the weak Hamiltonian transform similarly under CP and the amplitude for S"-'>Pt is non-zero in both