Nonmesonic weak decay of Lambda hypernuclei: The Lambda N-Sigma N coupling

摘要

The nonmesonic weak decay of Lambda hypernuclei is studied within a microscopic diagrammatic approach which is extended to include the Lambda N-Sigma N strong interaction coupling. We adopt a nuclear matter formalism which, through the local density approximation, allows us to model finite hypernuclei. One-meson-exchange potentials are used for the weak and strong four-baryon interactions. The rates for the neutron-and proton-induced weak decays, Lambda N -> nN and Lambda N -> Sigma N -> nN (N = n or p; Sigma = Sigma(-), Sigma(0), and Sigma(+)), are predicted for C-12(Lambda), Si-28(Lambda), Fe-56(Lambda), and Pb-208(Lambda). The Lambda N-Sigma N coupling turns out to provide a contribution of about 23% (5%) to the total neutron-induced rate (proton-induced rate). Again as an effect of the hyperon coupling, the total one-nucleon-induced rate increases by about 9%, while the Gamma(n)/Gamma(p) ratio increases by about 17%. The saturation property of the nonmesonic rates with increasing hypernuclear mass number is clearly obtained and explained. The above percentage modifications remain almost unaltered through the hypernuclear mass number. All the non-negligible changes introduced by the Lambda N-Sigma N coupling lead to a definite improvement of our predictions once compared with the available KEK and FINUDA data.