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Five-body cluster structure of double-$Λ$ hypernucleus $^{11}_{ΛΛ}$Be

Energy levels of the double $Λ$ hypernucleus, $^{11}_{ΛΛ}$Be are calculated within the framework of an $ααn ΛΛ$ five-body model. Interactions between constituent particles are determined so as to reproduce reasonably the observed low-energy properties of the $αα$, $ααn$ nuclei and the existing data for $Λ$-binding energies of the $αΛ$, $ααΛ$, $αn Λ$ and $ααn Λ$ systems. An effective $ΛΛ$ interaction is constructed so as to reproduce, within the $αΛΛ$ three-body model, the $B_{ΛΛ}$ of $^6_{ΛΛ}$He, which was extracted from the emulsion experiment, the NAGARA event. With no adjustable parameters for the $ααn ΛΛ$ system, $B_{ΛΛ}$ of the ground and bound excited states of $^{11}_{ΛΛ}$Be are calculated with the Gaussian Expansion Method. The Hida event, recently observed at KEK-E373 experiment, is interpreted as an observation of the ground state of the $^{11}_{ΛΛ}$Be.