DECAY MODES OF SIGMA-HYPERNUCLEI AND LAMBDA-HYPERNUCLEI

A review is presented of the problem of Σ and Λ decay in nuclei. By means of handy, yet reliable approximations, an approach to Σ decay is developed which allows a clear insight into the different aspects of the problem. The role of nuclear polarization, due to the spin-isospin ΣN → ΛN interaction, in the reduction of the Σ widths is discussed. Many experimentally observable Σ hypernuclei are predicted by showing that their widths are narrower than the separation energies between levels. The mesonic and non-mesonic decays of Λ hypernuclei are analyzed. The non-mesonic width is fairly well reproduced by simplified models for the ΛN → NN weak transition, but quantities like the ratio of proton to neutron induced Λ decay are highly sensitive to the models used. On the other hand, the mesonic width is very sensitive to the pion-nucleus optical potential and can be used to discriminate between different potentials which are equally suited to describe low energy pion-nucleon scattering. © 1990.