Disappearance of nuclear deformation in hypernuclei: A perspective from a beyond-mean-field study

Abstract

The previous mean-field calculation [Phys. Rev. C 78, 054311 (2008)] has shown that the oblate deformation in $^{28,30,32}\mathrm{Si}$ disappears when a $\mathrm{\ensuremath{\Lambda}}$ particle is added to these nuclei. Here, we investigate this phenomenon by taking into account the effects beyond the mean-field approximation. To this end, we employ the microscopic particle-rotor model based on the covariant density functional theory. We show that the deformation of $^{30}\mathrm{Si}$ does not completely disappear, even though it is somewhat reduced, after a $\mathrm{\ensuremath{\Lambda}}$ particle is added if the beyond-mean-field effect is taken into account. We also discuss the impurity effect of a $\mathrm{\ensuremath{\Lambda}}$ particle on the electric-quadrupole transition and show that an addition of a $\mathrm{\ensuremath{\Lambda}}$ particle leads to a reduction in the $B(E2)$ value, as a consequence of the reduction in the deformation parameter.