Structure of light hypernuclei

The structure of light hypernuclei with strangeness S=−1S=−1 and −2−2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of ΛΛ hypernuclei, ΣΣ hypernuclei and double ΛΛ hypernuclei. A variety of aspects of ΛΛ hypernuclei is demonstrated through a systematic study of pp-shell hypernuclei (Λ6He,Λ6Li, Λ7Li, Λ8Li, Λ8Be, Λ9Be, Λ13C) and sdsd-shell ones (Λ20Ne, Λ21Ne): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the ΛΛ particle which shrinks the size of nuclear core and thus reduces the BB(E2) value, and the halo and skin structures in Λ6He and Λ6Li etc. The typical light hypernucleus Λ9Be is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of Λ7Li, Λ9Be and Λ13C using GEM provide important information on the spin structure of the underlying ΛNΛN interaction, by comparing with recent experimental data from γγ-ray hypernuclear spectroscopy. The Λ–ΣΛ–Σ coupling effect is studied in Λ4H and Λ4He. The binding mechanism of Σ4He is discussed together with the possible existence of Σ7Li, emphasizing the fact that the study of Σ7Li is useful for extracting information on the ΣNΣN interaction differing from that from Σ4He. A systematic study of double-ΛΛ hypernuclei, constrained by the NAGARA   data (ΛΛ6He) within a four-body cluster model indicates that the recently observed Demachi–Yanagi   event can be interpreted as the 2+2+ state of ΛΛ10Be. The effect of hyperon mixing in ΛΛ6He and ΛΛ10Be is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the ss-hole in light nuclei, which is promising for understanding the production mechanism of double-ΛΛ and twin-ΛΛ hypernuclei via ΞΞ-atomic capture.