Weak radiative decays of hyperons: Quarks, SU(6)W, and vector-meson dominance.

Abstract

Quark-model, $\mathrm{SU}{(6)}_{W}$, and vector-dominance-model (VDM) methods are simultaneously used to investigate weak radiative decays of hyperons. The use of the VDM helps in the identification of the origin of the quark-model violation of the Hara theorem: besides the ${\overline{u}}_{1}{\ensuremath{\sigma}}_{\ensuremath{\mu}\ensuremath{\nu}}{\ensuremath{\gamma}}_{5}{q}^{\ensuremath{\nu}}{u}_{2}{A}^{\ensuremath{\mu}}$ term the ${A}_{\ensuremath{\mu}}{J}_{V}^{\ensuremath{\mu}}$ "contact" photon-quark interaction generates an additional contribution which is effectively equivalent to a nonvanishing ${\overline{u}}_{1}{\ensuremath{\gamma}}_{5}{\ensuremath{\gamma}}_{\ensuremath{\mu}}{u}_{2}{A}^{\ensuremath{\mu}}$ photon-hadron coupling. Our approach provides a $\mathrm{SU}{(6)}_{W}$-based symmetry connection between radiative and nonleptonic hyperon decays. As a result, a parameter-free symmetry prediction for asymmetries and branching ratios in weak radiative hyperon decays is obtained. The ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma}$ decay asymmetry is found to be large and negative ($\ensuremath{\alpha}\ensuremath{\simeq}\ensuremath{-}0.6$).