Direct experimental evidence of the weak $Lambda n p rightarrow n n p$ hypernucleus decay

A direct experimental evidence of the occurrence of the weak reaction $Lambda nprightarrow nnp$ in nuclei has been obtained by the FINUDA experiment. Three events have been found that can be attributed to $^{7}_{Lambda}$Li and $^{9}_{Lambda}$Be two nucleon-induced non mesonic weak decays. The kinematic analysis of such events is presented here.