Few-Body Aspects of Hypernuclear Physics

Recent development in the study of the structure of light Λ and double Λ hypernuclei is reviewed from the view point of few-body problems and interactions between the constituent particles. In the study the present author and collaborators employed Gaussian expansion method for few-body calculations; the method has been applied to many kinds of few-body systems in the fields of nuclear physics and exotic atomic/molecular physics. We reviewed the following subjects studied using the method: (1) Precise three- and four-body calculations of ⁷ _Λ He, ⁷ _Λ Li, ⁷ _Λ Be, ⁸ _Λ Li, ⁸ _Λ Be, ⁹ _Λ Be, ¹⁰ _Λ Be, ¹⁰ _Λ B and ¹³ _Λ C provide important information on the spin structure of the underlying ΛN interaction by comparing the calculated results with the recent experimental data by γ-ray hypernuclear spectroscopy. (2) The Λ-Σ coupling effect was investigated in ⁴ _Λ H and ⁴ _Λ He on the basis of the N + N + N + Λ (Σ) four-body model. (3) A systematic study of double-Λ hypernuclei and the ΛΛ interaction, based on the NAGARA event data (⁶ _ΛΛ He), was performed within the α + x + Λ + Λ cluster model (x = n, p, d, t,³He and α) and α + α + n + Λ + Λ cluster model, (4) The Demachi-Yanagi event was interpreted as observation of the 2⁺ state of ¹⁰ _ΛΛ Be, (5) The Hida event was interpreted as observation of the ground state of ¹¹ _ΛΛ Be.