Container structure of alpha-alpha-Lambda clusters in 9-Lambda-Beryrium

A new concept of clustering is discussed in A hypernuclei using a new-type microscopic cluster model wave function, which has a structure in which constituent clusters are confined in a container, whose size is a variational parameter and which we refer to as a hyper-Tohsaki-Horiuchi-Schuck-Röpke (hyper-THSR) wave function. By using the hyper-THSR wave function, the 2α + A-cluster structure in ⁹_ΛBe is investigated. We show that full microscopic solutions in the 2α + A-cluster system, which are given as 2α + A Brink-GCM (generator coordinate method) wave functions, are almost perfectly reproduced by the single configurations of the hyper-THSR wave function. The squared overlaps between both wave functions are calculated to be 99.5%, 99.4%, and 97.7% for J^π = 0⁺, 2+, and 4+ states, respectively. We also simulate the structural change by adding the A particle, by varying the ΛN interaction artificially. With the increase of the AN interaction, the A particle gets to move more deeply inside the core and strongly invokes the spatial core shrinkage. Accordingly, distinct localized 2α clusters appear in the nucleonic intrinsic density, though, in the ⁸Be nucleus, a gaslike 2α-cluster structure is shown. The origin of the localization is associated with the strong effect of the Pauli principle. We conclude that the container picture of the 2α and A clusters is essential in understanding the cluster structure in ⁹_ΛBe, in which the very compact spatial localization of clusters is shown in the density distribution.