Electromagnetic properties of 21O 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 21O, finding τ 1 / 2 + = 420 − 32 + 35 (stat) − 12 + 34 (sys) ps. This result together with the deduced level scheme and branching ratio of several γ-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 B ( E 2 ; 1 / 2 + → 5 / 2 g . s . + ) = 0.71 − 0.06 − 0.06 + 0.07 + 0.02 e2 fm4, 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.