Hypernuclear Weak Decays(Chapter III.,Hypernuclei and Baryon-Baryon Interaction)

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The recent theoretical studies of Λ-hypernuclear weak decays of the nonmesonic and π-mesonic ones are developed with the aim to disclose the link between the experimental decay observables and the underlying basic weak decay interactions and the weak decay mechanisms. The expressions of the nonmesonic decay rates Γ_<nm> and the decay asymmetry parameter α_1 of protons from the polarized hypernuclei are presented in the shell model framework. We then introduce the meson theoretical ΛN→NN interactions which include the one-meson exchanges, the correlated-2π exchanges, and the chiral-pair-meson exchanges. The features of meson exchange potentials and their roles on the nonmesonic decays are discussed. With the adoption of the π+2π/ρ+2π/σ+ω+K+ρπ/a_1+σπ/a_1 exchange potentials, we have carried out the systematic calculations of the nonmesonic decay observables for light-to-heavy hypernuclei. The present model can account for the available experimental data of the decay rates, Γ_n/Γ_p ratios, and the intrinsic asymmetry parameters α_Λ (α_Λ is related to α_1) of emitted protons well and consistently within the error bars. The hypernuclear lifetimes are evaluated by converting the total weak decay rates Γ_<tot>=Γ_π+Γ_<nm> to γ, which exhibit saturation property for the hypernuclear mass A≥30 and agree grossly well with experimental data for the mass range from light to heavy hypernuclei except for the very light ones. Future extensions of the model and the remaining problems are also mentioned. The π-mesonic weak processes are briefly surveyed, and the calculations and predictions are compared and confirmed by the recent high precision FINUDA π-mesonic decay data. This shows that the theoretical basis seems to be firmly grounded.
2010-11-30

Hypernuclear Weak Decays(Chapter III.,Hypernuclei and Baryon-Baryon Interaction)

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