Molecular Structures of Strangeness Light-nuclei and their Response Spectra

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1.Mean-field calculations for strangeness-nucleiHartree-Fock (HF) and Density-dependent Hartree-Fock (DDHF) calculations for hypernuclei are performed on the basis of ΝΝ and ΛΝ effective interactions with a finite-range. We discuss structures of ^<17>_ΛO and ^5_ΛHe and core-polarization effects arising from the addition of the Λ-hyperon. We stress that the core-polarization (rearrangement) energy ΔE_N is 〜2 MeV for (Os)_Λ and 〜1 MeV for (Op)_Λ in the DDHF. The reason why the total energy E_N of the core is reduced is because the nucleon s.p. energy e_α becomes deeper by the addition of the Λ. Energies of ΔE_N depend on the nature of the ΝΝ effective interaction and the capacity of the ΛΝ effective interaction to reproduce the experimental data.2.Production of strangeness-nuclei and their response spectraWe propose an "optimal Fermi-averaging approximation" to nuclear reactions within the DWIA. We apply it to calculate A quasi-free spectra from ^<12>C(π^+,K^+) reactions, and compare them with experimental data. The results show that the calculated spectra are in excellent agreements with the data, because the energy-dependence originates from the nature of the optimal Fermi-averaging t-matrix. Then we extend it (π^-,K^+) spectra on ^<12>C and ^<28>Si targets in order to extract properties of Σ^--nucleus potential from the data. We find that the Σ^--nucleus potential for ^<28>Si has a repulsion of V^0_Σ【similar or equal】 +20 〜 +40 MeV, and a sizable absorption of -10 〜 -30 MeV for a Woods-Saxon type potential, and that a Σ^--nucleus potential reproducing the Σ^-atomic x-ray data, would reproduce the (π^-,K^+) spectra. Moreover, we predict that the ^4_ΛHe ground state is populated by about 20% via Σ components in (stopped K^-,π^-) reactions, using a coupled (3Ν-Λ)+(3Ν-Σ) models.