Lambda Lambda-XiN Coupling Effects in Light Hypernuclei

Abstract

The significance of $ΛΛ$-$Ξ$N coupling in double-$Λ$ hypernuclei has been studied. The Pauli suppression effect due to this coupling in $^6_{ΛΛ}$He has been found to be 0.43 MeV for the coupling strength of the NSC97e potential. This indicates that the free-space $ΛΛ$ interaction is stronger by about $5^{\circ}$ phase shift than that deduced from the empirical data of $^6_{ΛΛ}$He without including the Pauli suppression effect. In $^5_{ΛΛ}$He and $^5_{ΛΛ}$H, an attractive term arising from $ΛΛ$-$Ξ$N conversion is enhanced by the formation of an alpha particle in intermediate $Ξ$ states. According to this enhancement, we have found that the $ΛΛ$ binding energy ($ΔB_{ΛΛ}$) of $^5_{ΛΛ}$He is about 0.27 MeV larger than that of $^6_{ΛΛ}$He for the NSC97e coupling strength. This finding deviates from a general picture that the heavier is the core nucleus, the larger is $ΔB_{ΛΛ}$.