Study of nuclei with strangeness

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The purpose of this research project is to discover the world of nuclei with strangeness and solve the various current problems in the strangeness nuclear physics. We have developed new experimental techniques and devices in order to perform high precision experiments on nuclei with s=-1 and to discover nuclei with s=-2. We have also organized a systematic theoretical study on strangeness nuclear physics along with the experimental programs. We have constructed a Ge-ball detector (Hyperball) for the γ-spectroscopy of hypernuclei. The M1 and E2 γ transitions ィイD17ィエD1LiィイD2ΛィエD2 and ィイD19ィエD1BeィイD2ΛィエD2 were clearly observed for the first time with Ge detectors. The spin-dependent fine-structures of hypernuclei were extensively studied with these new data. The lifetimes and decay branching ratios were also extensively measured for heavier hypernuclei which revealed new aspects of the ΛN weak interaction. It has been extensively studied with OBE and "quark" - model. The nuclei with s=-2 have been searched for with various methods such as a new hybrid-emulsion detector and a cylindrical π spectrometer (CDS) which were constructed in this research project. The experiments with these detectors were successfully carried out at KEK and BNL. The discovery of new s=-2 nuclei are quite probable. The evidence of Ξ-nuclei was already obtained. The hyperon-nucleon interaction has been studied both in quark models and OBE models. The Σ-p scattering experiments were also performed and provided new cross section data which should improve our understanding on hypernuclei.We have hosted 5 international and 8 domestic conferences to promote and organize the research on strangeness nuclear physics. More than 100 papers have been published in this research project.