Ab initio calculations of anomalous seniority breaking in the $\pi g_{9/2}$ shell for the $N=50$ isotones

Abstract

We performed \textit{ab initio} valence-space in-medium similarity renormalization group (VS-IMSRG) calculations based on chiral two-nucleon and three-nucleon interactions to investigate the anomalous seniority breaking in the neutron number $N=50$ isotones: ${}^{92}$Mo, ${}^{94}$Ru, ${}^{96}$Pd, and ${}^{98}$Cd. Our calculations well reproduced the measured low-lying spectra and electromagnetic $E2$ transitions in these nuclei, supporting partial seniority conservation in the first $\pi g_{9/2}$ shell. Recent experiments have revealed that, compared to the symmetric patterns predicted under the conserved seniority symmetry, the $4_1^{+}\to 2_1^{+}$ $E2$ transition strength in ${}^{94}$Ru is significantly enhanced and that in ${}^{96}$Pd is suppressed. In contrast, the $6_1^{+}\to 4_1^{+}$ and $8_1^{+}\to 6_1^{+}$ transitions exhibit the opposite trend. We found that this anomalous asymmetry is sensitive to subtle seniority breaking effects, providing a stringent test for state-of-the-art nucleon-nucleon interactions and nuclear models. We analyzed the anomalous asymmetry using VS-IMSRG calculations across various valence spaces. Our \textit{ab initio} results suggest that core excitations of both proton and neutron across the $Z=50$ shell are ascribed to the observed anomalous seniority breaking in the $N=50$ isotones.

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Cited by in corpus (5)

• Improving the predictive power of empirical shell-model Hamiltonians
• Ab initio study of island of inversion in odd-$A$ nuclei: Structure of ${}^{31,33}$Mg
• Partial conservation of seniority in semi-magic nuclei
• Evolution of shell structure at $\mathbf{N}=32$ and 34: Insights from realistic nuclear forces
• Electromagnetic Properties of the N=50 Isotones with the p35-i3 Hamiltonian