Microscopic description of triaxiality in Ru isotopes with covariant energy density functional theory

TL;DR

This study uses covariant energy density functional theory to microscopically analyze triaxial shapes in Ru isotopes, successfully reproducing experimental spectra and transition rates, and confirming the presence of triaxiality in low-lying states.

Contribution

It provides a detailed microscopic description of triaxiality in Ru isotopes using a five-dimensional collective Hamiltonian based on relativistic mean-field calculations.

Findings

Calculated spectra agree with experimental data.

Evidence supports triaxial shapes in Ru isotopes near $^{110}$Ru.

Transition rates match observed values.

Abstract

The triaxiality in nuclear low-lying states has attracted great interests for many years. Recently, the reduced transition probabilities for levels near the ground state in $^{110}$Ru have been measured and provided strong evidences for a triaxial shape of this nucleus. The aim of this work is to provide a microscopic study of low-lying states for the Ru isotopes with $A\sim100$ and to examine in detail the role of triaxiality, and the evolution of quadrupole shapes with the isospin and spin degrees of freedom. The low-lying excitation spectra and transition probabilities of even-even Ru isotopes are described at the beyond mean-field level by solving a five-dimensional collective Hamiltonian with parameters determined by constrained self-consistent mean-field calculations based on the relativistic energy density functional PC-PK1. The calculated energy surfaces, low-energy spectra, intraband and interband transition rates, as well as some characteristic collective observables, such as $E(4_{\rm g.s.}^+)/E(2^+_{\rm g.s.})$, $E(2^+_\gamma)/E(4^+_{\rm g.s.})$, $B(E2; 2^+_{\rm g.s.}\to 0^+_{\rm g.s.})$, and $\gamma$ band staggerings are in a good agreement with the available experimental data. The main features of the experimental low-lying excitation spectra and electric transition rates are well reproduced, and thus strongly support the onset of triaxiality in the low-lying excited states of the Ru isotopes around $^{110}$Ru.