THEORETICAL STUDY OF NUCLEI WITH STRANGENESS

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The project consists of five major subjects which lead to the following achievements. (1) The microscopic three- and four-body cluster model calculations have been carried out for spectroscopy of light hypernuclei : The shrinkage of the nuclear core under the effect of Λ participation has been confirmed. The role of spin-spin and spin-orbit ΛN interactions has been analysed. It has been revealed that the admixture of Σ component into the mass-4 Λ hypernuclear low-lying states has a characteristic role reflecting the properties of YN interaction adopted. The in-flight and stopped (K-, π) reaction spectra are successfully explained by the DWIA calculation. (2) Several theoretical attempts have been presented to evaluate the production rates of double-Λ hypernuclei. The effect of hyperon mixing has been also investigated in typical S = -2 systems. (3) It is remarkable that several meson theoretical models of new YN and YY interactions have been presented to be tested in the hypernuclear structure. Moreover the quark models also presented several versions of the baryon-baryon interactions. The quark model has been extended to evaluate the interaction of the H particles in nuclear matter. (4) In order to explain new experimental data of hypernuclear weak decays (lifetimes), the correlated two-pion exchange process and the direct (quark process were evaluated in addition to the OPE process. It has been found that they have both certain favorable effects but are not always sufficient. (5) The important calculational methods have been applied and developed in the research project : the typical examples are the quantum molecular dynamics (QMD) approach, the Gaussian basis coupled-rearrangement channel method and the complex scaling method.