Coupling shape and pairing vibrations in a collective Hamiltonian based on nuclear energy density functionals (II): low-energy excitation spectra of triaxial nuclei

TL;DR

This paper extends a nuclear collective Hamiltonian to include pairing vibrations, improving the modeling of low-energy spectra and transition rates in triaxial nuclei by coupling shape and pairing degrees of freedom.

Contribution

It introduces a coupled shape and pairing vibrational model based on energy density functionals, enhancing the description of low-energy nuclear spectra.

Findings

Including pairing vibrations improves agreement with experimental spectra.

Coupling between shape and pairing degrees of freedom affects transition rates.

Zero-point energy corrections influence low-lying excitation energies.

Abstract

The triaxial quadrupole collective Hamiltonian, based on relativistic energy density functionals, is extended to include a pairing collective coordinate. In addition to triaxial shape vibrations and rotations, the model describes pairing vibrations and the coupling between triaxial shape and pairing degrees of freedom. The parameters of the collective Hamiltonian are determined by a covariant energy density functional, with constraints on the intrinsic triaxial shape and pairing deformations. The effect of coupling between triaxial shape and pairing degrees of freedom is analyzed in a study of low-lying spectra and transition rates of $^{128}$Xe. When compared to results obtained with the standard triaxial quadrupole collective Hamiltonian, the inclusion of dynamical pairing compresses the low-lying spectra and improves interband transitions, in better agreement with data. The effect of zero-point energy (ZPE) correction on low-lying excited spectra is also discussed.