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

New spectra from the FINUDA experiment of the Non-Mesonic Weak Decay (NMWD) proton kinetic energy for BeΛ9, BΛ11, CΛ12, CΛ13, NΛ15 and OΛ16 are presented and discussed along with the published data on HeΛ5 and LiΛ7. 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 Γ/Γ=0.43±0.25 is determined for the first time. A value for the two-nucleon stimulated decay rate to the total decay rate Γ/Γ=0.24±0.10 is also extracted.