Proton spectra from Non-Mesonic Weak Decay of p-shell Λ-hypernuclei and evidence for the two-nucleon induced process

Exploiting the large mass number range and the low energy threshold (15 MeV) for the proton detection of FINUDA, an evaluation of both Final State Interactions (FSI) and the two-nucleon induced NMWD contributions to the decay process has been done. Based on this evaluation, a linear dependence of FSI on the hypernuclear mass number A is found and for the two-nucleon stimulated decay rate the experimental value of Γ2/Γp=0.43±0.25 is determined for the first time. A value for the two-nucleon stimulated decay rate to the total decay rate Γ2/ΓNMWD=0.24±0.10 is also extracted.