Impurity effect of Lambda hyperon on collective excitations of nuclear core in 25ΛMg

Taking the ground state rotational band in Mg-24 as an example, we investigate the impurity effect of Lambda hyperon on collective excitations of atomic nuclei in the framework of non-relativistic energy density functional theory. To this end, we take into account correlations related to the restoration of broken symmetries and fluctuations of collective variables by solving the eigenvalue problem of a five-dimensional collective Hamiltonian for quadrupole vibrational and rotational degrees of freedom. The parameters of the collective Hamiltonian are determined with constrained mean-field calculations for triaxial shapes using the SGII Skyrme force. We compare the low-spin spectrum for Mg-24 with the spectrum for the same nucleus inside Mg-25(Lambda). It is found that the Lambda hyperon stretches the ground state band and reduces the B(E2 : 2(1)(+) -> 0(1)(+)) value by similar to 9%, mainly by softening the potential energy surface towards the spherical shape, even though the shrinkage effect on the average proton radius is only similar to 0.5%. (C) 2011 Elsevier B.V. All rights reserved.