Landscape of pear-shaped even-even nuclei

Background: The phenomenon of reflection-asymmetric nuclear shapes is relevant to nuclear stability, nuclear spectroscopy, nuclear decays and fission, and the search for new physics beyond the standard model. Global surveys of ground-state octupole deformation, performed with a limited number of models, suggest that the number of pear-shaped isotopes is fairly limited across the nuclear landscape.Purpose: We carry out a global analysis of ground-state octupole deformations for particle-bound even-even nuclei with $Z\ensuremath{\le}110$ and $N\ensuremath{\le}210$ using nuclear density functional theory (DFT) with several nonrelativistic and covariant energy density functionals. In this way, we can identify the best candidates for reflection-asymmetric shapes.Methods: The calculations are performed in the frameworks of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory and relativistic Hartree-Bogoliubov theory using DFT solvers employing harmonic oscillator basis expansion. We consider five Skyrme and four covariant energy density functionals.Results: We predict several regions of ground-state octupole deformation. In addition to the ``traditional'' regions of neutron-deficient actinide nuclei around $^{224}\mathrm{Ra}$ and neutron-rich lanthanides around $^{146}\mathrm{Ba}$, we identified vast regions of reflection-asymmetric shapes in very neutron-rich nuclei around $^{200}\mathrm{Gd}$ and $^{288}\mathrm{Pu}$, as well as in several nuclei around $^{112}\mathrm{Ba}$. Our analysis suggests several promising candidates with stable ground-state octupole deformation, primarily in the neutron-deficient actinide region, that can be reached experimentally. Detailed comparison between Skyrme and covariant models is performed.Conclusions: Octupole shapes predicted in this study are consistent with the current experimental information. This work can serve as the starting point of a systematic search for parity doublets in odd-mass and odd-odd nuclei, which will be of interest in the context of new physics searches.

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