Fully Coupled Channel Approach to Doubly Strange s -Shell Hypernuclei

We describe ab initio calculations of doubly strange, S=-2, s-shell hypernuclei (_ΛΛ⁴H, _ΛΛ⁵H, _ΛΛ⁵He, and _ΛΛ⁶He) as a first attempt to explore the few-body problem of the full-coupled channel scheme for these systems. The wave function includes ΛΛ, ΛΣ, NΞ, and ΣΣ channels. Minnesota $NN$, D2^' $YN$, and simulated $YY$ potentials based on the Nijmegen hard-core model are used. Bound-state solutions of these systems are obtained. We find that a set of phenomenological B₈B₈ interactions among the octet baryons in S=0,-1, and -2 sectors, which is consistent with all of the available experimental binding energies of S=0,-1, and -2 s-shell (hyper)nuclei, can predict a particle stable bound state of _ΛΛ⁴H. For _ΛΛ⁵H and _ΛΛ⁵He, ΛN-ΣN and ΞN-ΛΣ potentials significantly affect the net ΛΛ-NΞ coupling, and a large Ξ probability is obtained even for a weaker ΛΛ-NΞ potential.