Structure of light hypernuclei

The structure of light hypernuclei with strangeness S = - 1 and - 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 Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (Λ6 He,Λ6 Li, Λ7 Li, Λ8 Li, Λ8 Be, Λ9 Be, Λ13 C) and s d-shell ones (Λ20 Ne, Λ21 Ne): 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 Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in Λ6 He and Λ6 Li etc. The typical light hypernucleus Λ9 Be is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of Λ7 Li, Λ9 Be and Λ13 C using GEM provide important information on the spin structure of the underlying Λ N interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ - Σ coupling effect is studied in Λ4 H and Λ4 He. The binding mechanism of Σ4 He is discussed together with the possible existence of Σ7 Li, emphasizing the fact that the study of Σ7 Li is useful for extracting information on the Σ N interaction differing from that from Σ4 He. A systematic study of double-Λ hypernuclei, constrained by the NAGARA data (Λ Λ6 He) within a four-body cluster model indicates that the recently observed Demachi-Yanagi event can be interpreted as the 2+ state of Λ Λ10 Be. The effect of hyperon mixing in Λ Λ6 He and Λ Λ10 Be is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S = - 2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture. © 2009 Elsevier B.V. All rights reserved.