Abstract
Background: The hyperon impurity effect in nuclei has been extensively studied in different mean-field models. Recently, there is a controversy about whether the hyperon is more tightly bound in the normal deformed (ND) states than that in the superdeformed (SD) states.
Purpose: This article is aimed to provide a beyond-mean-field study of the low-lying states of hypernuclei with shape coexistence and to shed some light on the controversy.
Method: The models of relativistic mean field and beyond based on a relativistic point-coupling energy functional are adopted to study the low-lying states of both and . The wave functions of low-lying states are constructed as a superposition of a set of relativistic mean-field states with different values of quadrupole deformation parameter. The projections onto both particle number and angular momentum are considered.
Results: The binding energies in both ND and SD states of are studied in the case of the hyperon occupying the , or state in the spherical limit, respectively. For comparison, four sets of nucleon-hyperon point-coupling interactions are used, respectively. Moreover, the spectra of low-lying states in and are calculated based on the same nuclear energy density functional. The results indicate that the SD states exist in for all four effective interactions. Furthermore, the reduces the quadrupole collectivity of ND states to a greater extent than that of SD states. For , the beyond-mean field decreases the binding energy of the SD state by 0.17 MeV, but it almost has no effect on that of the ND state.
Conclusions: In , the and binding energies of the SD states are always larger than those of the ND states. For , the conclusion depends on the effective nucleon-hyperon interaction. Moreover, the beyond-mean-field model calculation indicates that the hyperon is less bound in the SD state than that in the ND state.
5 More- Received 16 November 2016
DOI:https://doi.org/10.1103/PhysRevC.95.034309
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