Bound States and Molecular Structure of Systems with Hyperons

Abstract

Microscopic calculations are done for ∑-hypernuclear few-body systems by a method named ATMS. Among two-to five-body systems, only the ⁴_∑ He(0⁺) and ⁴_∑ H(0⁺) hypernuclei are expected to be bound: The binding energy and the width of the former are calculated to be 3.7 ~ 4.6 MeV and 4.5 ~ 7.9 MeV, respectively. The observation of ⁴_∑ He at KEK is in good agreement with the above prediction. The nucleus-∑ potential has a strong Lane term and a repulsive bump at short distance. The Lane term makes the system bound and the bump suppresses the ∑N-ΛN conversion. X-ray measurement of level shifts in the ⁴He-∑^-, ³He-∑^- and ³H-E^- atoms can provide another information on the Lane term.

In ²⁰⁸Pb, there may exist a peculiar state, Coulomb-assisted (atom-nucleus) hybrid state, where ∑^- is trapped in the surface region by the strong interaction with the aid of the inner centrifugal repulsion and the outer Coulomb attraction.

An analysis is given for new data of Ξ^-·12C atomic or nuclear systems from the emulsion-counter experiment at KEK. The double-Λ hypernucleus formation rate is calculated for a stopped Ξ^- on ⁴He. A high branching ratio of 37% is obtained for the ⁴_ΛΛ H formation from a Ξ^- ·⁴He atom. The detection of about 2.3 MeV neutron is proposed to search for lightest double-Λ hypernucleus ⁴_ΛΛ H.