Electromagnetic properties of ${}^{21}$O for benchmarking nuclear Hamiltonians

Abstract

The structure of exotic nuclei provides valuable tests for state-of-the-art nuclear theory. In particular electromagnetic transition rates are more sensitive to aspects of nuclear forces and many-body physics than excitation energies alone. We report the first lifetime measurement of excited states in ${}^{21}$O, finding ${\tau }_{1/2^{+}}=420_{-32}^{+35}{\text{(stat)}}_{-12}^{+34}\text{(sys)}$\,ps. This result together with the deduced level scheme and branching ratio of several $\gamma$-ray decays are compared to both phenomenological shell-model and ab initio calculations based on two- and three-nucleon forces derived from chiral effective field theory. We find that the electric quadrupole reduced transition probability of $\mathrm{B}(E2;1/2^{+}\to 5/2_{g.s.}^{+})=0.71_{-0.06-0.06}^{+0.07+0.02}$~e${}^2$fm${}^4$, derived from the lifetime of the $1/2^{+}$ state, is smaller than the phenomenological result where standard effective charges are employed, suggesting the need for modifications of the latter in neutron-rich oxygen isotopes. We compare this result to both large-space and valence-space ab initio calculations, and by using multiple input interactions we explore the sensitivity of this observable to underlying details of nuclear forces.

arXiv comment23 pages, 3 figures

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