A Theoretical Determination of Nnn/Nnp in Hypernuclear Non--Mesonic Weak Decay
Abstract
The ratio Nnn/Nnp between the number of neutron-neutron and neutron--proton pairs emitted in the non--mesonic weak decay of -hypernuclei is calculated within a nuclear matter formalism extended to 12LambdaC via the local density approximation. The single--nucleon emission spectra, Np and Nn, are also evaluated. Our formalism takes care of both ground state correlations (gsc) and final state interactions (FSI). The evaluation of Nnn/Nnp which, unlike Gamman/Gammap = Gamma(Lambda n -> nn)/Gamma(Lambda p -> np), is an actual observable quantity in non--mesonic decay is performed within a fully microscopic model where a proper treatment of FSI, gsc and ground state normalization is considered. All the isospin channels contributing to one-- and two--nucleon induced decays are included. Our final result for the coincidence number ratio, Nnn/Nnp=0.374, is in agreement with the KEK--E508 datum, (Nnn/Nnp) exp=0.40 +/- 0.10.