Direct experimental evidence of the weak $\mathrm{\Lambda }np\to nnp$ hypernucleus decay

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