Non-mesonic weak decay of Λ-hypernuclei and the final state interaction

In spite of the recent progresses achieved at BNL and KEK, a consistent understanding of the non-mesonic weak decay is yet to be achieved. The rapid saturation of total decay rate in its mass dependence, Γn/Γp ratio puzzle, opposite sign of decay asymmetry parameter between Λ5He and Λ12C, and ΔI=1/2 rule of non-mesonic weak decay are the current concerns, but not understood yet. The difficulties are largely in the treatment of the final state interaction. In the paper, we discuss on the role of final state interaction in the interpretation of the newly measured decay particle spectra in the non-mesonic weak decay of Λ hypernuclei.