Hypernuclear weak decay puzzle
A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed. It involves a partial wave expansion of the emitted nucleon waves, preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case t...
Guardado en:
| Autores principales: | , , , , , |
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| Formato: | Articulo |
| Lenguaje: | Inglés |
| Publicado: |
2002
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| Materias: | |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/125943 |
| Aporte de: |
| Sumario: | A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed. It involves a partial wave expansion of the emitted nucleon waves, preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case the weak Λ-core coupling formalism. The extreme particle-hole model and the quasiparticle Tamm-Dancoff approximation are explicitly worked out. It is shown that the nuclear structure manifests itself basically through the Pauli principle, and a very simple expression is derived for the neutron- and proton-induced decays rates Γ<sub>n</sub> and Γ<sub>p</sub>, which does not involve the spectroscopic factors. We use the standard strangeness-changing weak ΛN→NN transition potential which comprises the exchange of the complete pseudoscalar and vector meson octets (π,η,K,ρ,ω,K*), taking into account some important parity-violating transition operators that are systematically omitted in the literature. The interplay between different mesons in the decay of ¹²<sub>Λ</sub>C is carefully analyzed. With the commonly used parametrization in the one-meson-exchange model (OMEM), the calculated rate Γ<sub>NM</sub> = Γ<sub>n</sub> + Γ<sub>p</sub> is of the order of the free Λ decay rate Γ⁰(Γ<sup>th</sup><sub>NM</sub> ≅ Γ⁰) and is consistent with experiments. Yet the measurements of Γ<sub>n/p</sub> = Γ<sub>n</sub> / Γ<sub>p</sub> and of Γ<sub>p</sub> are not well accounted for by the theory (Γ<sup>th</sup><sub>n/p</sub> ≲ 0.42,Γ<sup>th</sup><sub>p</sub> ≳ 0.60Γ⁰). It is suggested that, unless additional degrees of freedom are incorporated, the OMEM parameters should be radically modified. |
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