Abstract
Background: The impurity effect of hyperons on atomic nuclei has received a renewed interest in nuclear physics since the first experimental observation of appreciable reduction of transition strength in low-lying states of the hypernucleus . Many more data on low-lying states of hypernuclei will be measured soon for -shell nuclei, providing good opportunities to study the impurity effect on nuclear low-energy excitations.
Purpose: We carry out a quantitative analysis of the hyperon impurity effect on the low-lying states of -shell nuclei at the beyond-mean-field level based on a relativistic point-coupling energy density functional (EDF), considering that the hyperon is injected into the lowest positive-parity () and negative-parity () states.
Method: We adopt a triaxially deformed relativistic mean-field (RMF) approach for hypernuclei and calculate the binding energies of hypernuclei as well as the potential-energy surfaces (PESs) in the deformation plane. We also calculate the PESs for the hypernuclei with good quantum numbers by using a microscopic particle rotor model (PRM) with the same relativistic EDF. The triaxially deformed RMF approach is further applied in order to determine the parameters of a five-dimensional collective Hamiltonian (5DCH) for the collective excitations of triaxially deformed core nuclei. Taking and as examples, we analyze the impurity effects of and on the low-lying states of the core nuclei.
Results: We show that increases the excitation energy of the state and decreases the transition strength from this state to the ground state by . On the other hand, tends to develop pronounced energy minima with larger deformation, although it modifies the collective parameters in such a way that the collectivity of the core nucleus can be either increased or decreased.
Conclusions: The quadrupole deformation significantly affects the binding energies of deformed hypernuclei. A beyond-mean-field approach with the dynamical correlations due to restoration of broken symmetries and shape fluctuation is essential in order to study the impurity effect in a quantitative way.
11 More- Received 13 December 2014
- Revised 5 February 2015
DOI:https://doi.org/10.1103/PhysRevC.91.024327
©2015 American Physical Society