Three- and four-body structure of light hypernuclei and γ ray spectroscopy

Since YN scattering data are extremely limited, previously proposed YN interactions include much ambiguity. To elucidate the properties of YN interactions, it seems helpful to study the hypernuclear structures. This study was aimed to make such a structural study using a newly developed method for four-body calculation. Four-body calculation within the framework of 3N+Λ model in which ΣN channel contribution is renormalized into ΛN interaction was described in this report. Although the structural study of Λ3H is usable, Λ3H was considered to be unsuitable for the study of spin-spin force since Λ3H is a very weakly bound system and one of spin-doublets has not yet been observed. Therefore, a variational method using Jacobian coordinate Gaussian basis functions was employed. This method was useful in describing the short-range correlations and the long-range tail behavior. Thus, it was indicated that Λ4H and Λ4He are very useful hypernuclei for obtaining informations on the spin-spin part of ΛN interactions from the analysis of O+ - 1+ splitting. (M.N.)