Five-Body Cluster Structure of the Double-Λ Hypernucleus ΛΛ11Be

Energy levels of the double Lambda hypernucleus, Be-11(Lambda Lambda) are calculated within the framework of a alpha alpha n Lambda Lambda five-body model. Interactions between constituent particles are determined so as to reproduce reasonably the observed low-energy properties of the alpha alpha, alpha alpha n nuclei and the existing data for Lambda-binding energies of the alpha Lambda, alpha alpha Lambda, alpha n Lambda, and alpha alpha n Lambda systems. An effective Lambda Lambda interaction is constructed so as to reproduce, within the alpha Lambda Lambda three-body model, the B-Lambda Lambda of He-6(Lambda Lambda), which was extracted from the emulsion experiment, the NAGARA event. With no adjustable parameters for the alpha alpha n Lambda Lambda system, B-Lambda Lambda of the ground and bound excited states of Be-11(Lambda Lambda) 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 Be-11(Lambda Lambda).