Nonmesonic weak decay spectra of light hypernuclei

The nonmesonic weak decay spectra of light hypernuclei have been evaluated in a systematic way. As theoretical framework we adopt the independent particle shell model with three different one-meson-exchange transition potentials. Good agreement with data is obtained for proton and neutron kinetic energy spectra of $^4_\Lambda$He, and $^5_\Lambda$He, when the recoil effect is considered. The coincidence spectra of proton-neutron pairs are also accounted for quite reasonably, but it was not possible to reproduce the data for the neutron-neutron pair spectra. It is suggested that the $\pi+K$ meson-exchange model with soft monopole form factors could be a good starting point for describing the dynamics responsible for the decays of these two hypernuclei. The $^4_\Lambda$H~ spectra are also presented.