Non-mesonic weak decay of Λ-hypernuclei: a new determination of the [formula omitted] ratio

Abstract

Theoretical descriptions of the non-mesonic weak decay of Λ-hypernuclei are unable to reproduce the experimental values of the ratio Γ n / Γ p ≡ Γ ( Λ n → n n ) / Γ ( Λ p → n p ) . In this contribution we discuss a new approach to this problem. We have incorporated a one-meson-exchange model for the Λ N → n N transition in finite nuclei in an intranuclear cascade code for the calculation of double-coincidence nucleon distributions corresponding to the non-mesonic decay of 5 Λ He and 12 Λ C. The two-nucleon induced decay mechanism, Λ n p → n n p , 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 5 Λ He allows us to extract Γ n / Γ p = 0.39 ± 0.11 when the two-nucleon induced channel is neglected (i.e., Γ 2 = 0 ) and Γ n / Γ p = 0.26 ± 0.11 when Γ 2 / Γ 1 = 0.2 .