A Theoretical Determination of N_{nn}/N_{np} in Hypernuclear Non--Mesonic Weak Decay

TL;DR

This paper presents a microscopic theoretical calculation of the N_{nn}/N_{np} ratio in hypernuclear non-mesonic weak decay, incorporating correlations and interactions, and finds results consistent with experimental data.

Contribution

The study introduces a comprehensive microscopic model that accurately predicts the N_{nn}/N_{np} ratio, including all relevant isospin channels and effects like FSI and gsc.

Findings

Calculated N_{nn}/N_{np} ratio is 0.374.

Results agree with KEK-E508 experimental data.

Includes all isospin channels in the decay process.

Abstract

The ratio N_{nn}/N_{np} between the number of neutron-neutron and neutron--proton pairs emitted in the non--mesonic weak decay of \Lambda-hypernuclei is calculated within a nuclear matter formalism extended to ^{12}_{Lambda}C via the local density approximation. The single--nucleon emission spectra, N_p and N_n, are also evaluated. Our formalism takes care of both ground state correlations (gsc) and final state interactions (FSI). The evaluation of N_{nn}/N_{np} which, unlike Gamma_n/Gamma_p = 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, N_{nn}/N_{np}=0.374, is in agreement with the KEK--E508 datum, (N_{nn}/N_{np})^{\rm exp}=0.40 +/- 0.10.