Non-mesonic weak decay of Λ-hypernuclei: a new determination of the Γn/Γp ratio

Theoretical descriptions of the non-mesonic weak decay of Λ-hypernuclei are unable to reproduce the experimental values of the ratio Γn/Γp=Γ(Λn->nn)/Γ(Λp->np). In this contribution we discuss a new approach to this problem. We have incorporated a one-meson-exchange model for the ΛN->nN transition in finite nuclei in an intranuclear cascade code for the calculation of double-coincidence nucleon distributions corresponding to the non-mesonic decay of 5ΛHe and 12ΛC. The two-nucleon induced decay mechanism, Λnp->nnp, has been taken into account within a local density approximation scheme using a one-pion-exchange model supplemented by short range correlations. A weak decay model independent analysis of preliminary KEK coincidence data for 5ΛHe allows us to extract Γn/Γp=0.39+/-0.11 when the two-nucleon induced channel is neglected (i.e., Γ2=0) and Γn/Γp=0.26+/-0.11 when Γ2/Γ1=0.2