Ab Initio Emergence and Collapse of Nuclear Collectivity near N = Z = 40

Abstract

We present an \textit{ab initio} description of the emergence and collapse of enhanced quadrupole collectivity in nuclei near N=Z=40 using multi-shell valence-space Hamiltonians derived from chiral two- and three-nucleon forces with the in-medium similarity renormalization group. Projected generator-coordinate calculations with consistently evolved E2 operators capture the strong collectivity in ⁸⁰Zr and its decrease toward ⁸⁶Mo and ⁸⁸Ru without empirical effective charges. While the N,Z=40 effective single-particle energy gaps remain open, the 1g_9/2--2d_5/2 spacing is smallest near ⁷⁶Sr and ⁸⁰Zr, with its variation governed mainly by the proton-neutron monopole contribution. The associated occupancies are consistent with quadrupole correlations involving pseudo-SU(3) pf holes and quasi-SU(3) particles. Excluding the occupation of the proton and neutron 2d_5/2 from the variational space strongly suppresses the deformation and B(E2;2₁⁺→0₁⁺) in ⁸⁰Zr. These results mark a steady step toward \textit{ab initio} computations of heavy open-shell nuclei.

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BibTeX

@misc{cao2026initio,
  title = {{Ab Initio Emergence and Collapse of Nuclear Collectivity near N = Z = 40}},
  author = {X. C. Cao and C. F. Jiao and R. Z. Hu},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.15774},
  eprint = {2609.15774},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.15774},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Ab Initio Emergence and Collapse of Nuclear Collectivity near N = Z = 40
AU  - X. C. Cao
AU  - C. F. Jiao
AU  - R. Z. Hu
PY  - 2026
DA  - 2026/09/15
PB  - arXiv
DO  - 10.48550/arxiv.2609.15774
UR  - https://arxiv.org/abs/2609.15774
AB  - We present an \textit{ab initio} description of the emergence and collapse of enhanced quadrupole collectivity in nuclei near N=Z=40 using multi-shell valence-space Hamiltonians derived from chiral two- and three-nucleon forces with the in-medium similarity renormalization group. Projected generator-coordinate calculations with consistently evolved E2 operators capture the strong collectivity in ^80Zr and its decrease toward ^86Mo and ^88Ru without empirical effective charges. While the N,Z=40 effective single-particle energy gaps remain open, the 1g_9/2--2d_5/2 spacing is smallest near ^76Sr and ^80Zr, with its variation governed mainly by the proton-neutron monopole contribution. The associated occupancies are consistent with quadrupole correlations involving pseudo-SU(3) pf holes and quasi-SU(3) particles. Excluding the occupation of the proton and neutron 2d_5/2 from the variational space strongly suppresses the deformation and B(E2;2_1^+→0_1^+) in ^80Zr. These results mark a steady step toward \textit{ab initio} computations of heavy open-shell nuclei.
ER  -

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