NONMESONIC WEAK DECAY OF LAMBDA-HYPERNUCLEI

The non-mesonic decay modes of Lambda hypernuclei are examined. The on e-nucleon induced decay (Lambda N --> NN) is studied in a shell-model framework using a meson-exchange picture. The total decay rates and pa rity-violating asymmetries reproduce the available experimental data. However, the model does not yet explain the partial rates and the resu lting neutron- to proton-induced ratio Gamma(n)/Gamma(p). The two-nucl eon-induced decay rate (Lambda NN --> NNN) is evaluated using the prop agator formalism and the local-density approximation and is found to c ontribute about 15% to the total decay width of medium to heavy hypern uclei. The influence of this channel on the experimental determination of the ratio Gamma(n)/Gamma(p) is examined. The spectra of protons an d neutrons from each weak-decay mechanism have been obtained using a M onte Carlo simulation.