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

TL;DR

This study revises previous mean-field predictions by using a beyond-mean-field approach to show that nuclear deformation in hypernuclei like $^{30}$Si is only partially suppressed by a $ ext{Lambda}$ particle, affecting electric quadrupole transitions.

Contribution

It introduces a beyond-mean-field microscopic particle-rotor model based on covariant density functional theory to analyze hypernuclear deformation effects.

Findings

Deformation in $^{30}$Si is reduced but not eliminated by a $ ext{Lambda}$ particle.

The $ ext{Lambda}$ particle decreases the $B(E2)$ value, indicating reduced nuclear deformation.

Beyond-mean-field effects alter previous mean-field predictions about hypernuclear shape changes.

Abstract

The previous mean-field calculation [Myaing Thi Win and K. Hagino, Phys. Rev. C{\bf 78}, 054311 (2008)] has shown that the oblate deformation in $^{28,30,32}$Si disappears when a $\Lambda$ particle is added to these nuclei. We here 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 $^{30}$Si does not completely disappear, even though it is somewhat reduced, after a $\Lambda$ particle is added if the beyond-mean-field effect is taken into account. We also discuss the impurity effect of $\Lambda$ particle on the electric quadrupole transition, and show that an addition of a $\Lambda$ particle leads to a reduction in the $B(E2)$ value, as a consequence of the reduction in the deformation parameter.