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

A new concept of clustering is discussed in Lambda 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-Ropke (hyper-THSR) wave function. By using the hyper-THSR wave function, the 2 alpha + Lambda-cluster structure in Be-9(Lambda) is investigated. We show that full microscopic solutions in the 2 alpha + Lambda-cluster system, which are given as 2 alpha + Lambda 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(pi) = 0(+), 2(+), and 4(+) states, respectively. We also simulate the structural change by adding the Lambda particle, by varying the Lambda N interaction artificially. With the increase of the Lambda N interaction, the Lambda particle gets to move more deeply inside the core and strongly invokes the spatial core shrinkage. Accordingly, distinct localized 2 alpha clusters appear in the nucleonic intrinsic density, though, in the Be-8 nucleus, a gaslike 2 alpha-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 2 alpha and Lambda clusters is essential in understanding the cluster structure in Be-9(Lambda), in which the very compact spatial localization of clusters is shown in the density distribution.