Pi-mesonic and Nonmesonic Weak Decays of Double-Lambda Hypernuclei

研究了双-Λ超核π介子和非介子弱衰变的衰变机理、衰变速率和激发谱。双-Λ超核的非介子弱衰变存在两种模式，即核子诱导的弱衰变和超子诱导的弱衰变。我们已经证明，除了1π之外，相关的-2π交换（2π/σ和2π/ρ）相互作用对于理解核子诱导的ΛN→NN衰变也很重要。此外，我们将ω和K交换纳入我们的模型中。我们的衰变相互作用模型可以很好地解释单个-Λ超核的衰变速率和衰变速率比Γ_n/Γ_p。用介子交换相互作用模型计算了^6_<ΛΛ>He的核诱导衰变速率。计算出的衰变率小于^5_Λhe的两倍，这可能与^6_<ΛΛ>He.3中的ΛΛ-cluster结构效应有关。超子诱导的ΛΛ→Nλ和ΛΛ→P？N ^ - ?^Ο是在双-Λ超核中发现的新模式。我们推导了介子交换的衰变相互作用势。2π/σ、1ω和1K交换对theΛΛ→Nλ电位有贡献，而1π、2π/ρ和1K交换对theΛΛ→NΣ电位有贡献。采用这些势可以计算出^6_<ΛΛ>He和^<10>_<ΛΛ>Be的衰变率分别为自由Λ衰变率的5%和3%。超子诱导的双-Λ超核的衰变速率将在未来的实验中被探测到。重新讨论了^6_<ΛΛ>He和^<10>_<ΛΛ>Be的介子谱和π衰变率。新计算了^<10>_<ΛΛ>Be的π^-和π^Ο激发谱。从母超核基态通过自旋非翻转跃迁到达的低1^-态被强烈激发并形成尖锐的峰。这些特征可用于识别双重-Λ超核形成和/或确定子超核的自旋。

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.