| Research Abstract |
The decay mechanism, decay rates and excitation spectra of π-mesonic and nonmesonic weak decays of double-Λ hypernuclei have been studied.
1. Two decay modes exist in the nonmesonic weak decays of the double-Λ hypernuclei, I. e., the nucleon-induced weak decay and the hyperon-induced one. We have shown that the correlated-2π exchange (2π/σ and 2π/ρ) interactions in addition to the 1π are important in understanding the nucleon-induced ΛN→NN decays. Further we incorporate the ω and K exchanges in our model. Our decay interaction model can explain the decay rates and the decay rate ratios Γ_n/Γ_p of single-Λ hypernuclei well.
2. The meson-exchange interaction model is applied to evaluate the nucleon-induced decay rate of ^6_<ΛΛ>He. Calculated decay rate is found to be smaller than twice that of ^5_Λhe, which may be related to the ΛΛ-cluster structure effect in ^6_<ΛΛ>He.
3. The hyperon-induced ΛΛ→Nλ and ΛΛ→P?^-, N?^Ο are new modes seen in the double-Λ hypernuclei. We have derived the decay interaction potentials based on the meson exchanges. The 2π/σ, 1ω and 1K exchanges contribute to theΛΛ→Nλ potential, while the 1π, 2π/ρ and 1K exchanges do to theΛΛ→NΣ one. By adopting these potentials the decay rates of ^6_<ΛΛ>He and ^<10>_<ΛΛ>Be are evaluated to be 5% and 3% of the free Λ decay rate, respectively. The hyperon-induced decay rates of the double-Λ hypernuclei would be detectable in the future experiments.
4. The pion spectra and the π-decay rates of ^6_<ΛΛ>He and ^<10>_<ΛΛ>Be are re-discussed. The π^- and π^Ο excitation specta of ^<10>_<ΛΛ>Be are newly calculated. The low-lying 1^- states reached via the spin-nonflip transitions from the parent hypernuclear ground state are strongly excited and form the sharp peaks. Such characteristics may be utilized to identify the double-Λ hypernuclear formation and/or to determine the spins of danghter hypernuclei.
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