High-precision spectroscopy of ${}^{20}$O benchmarking ab-initio calculations in light nuclei

Abstract

The excited states of unstable ${}^{20}$O were investigated via ${\hat{I}}^3$-ray spectroscopy following the ${}^{19}$O$(d,p{)}^{20}$O reaction at 8 $A$MeV. By exploiting the Doppler Shift Attenuation Method, the lifetime of the 2${}_2^{+}$ and 3${}_1^{+}$ states were firmly established. From the ${\hat{I}}^3$-ray branching and E2/M1 mixing ratios for transitions deexciting the 2${}_2^{+}$ and 3${}_1^{+}$ states, the B(E2) and B(M1) were determined. Various chiral effective field theory Hamiltonians, describing the nuclear properties beyond ground states, along with a standard USDB interaction, were compared with the experimentally obtained data. Such a comparison for a large set of ${\hat{I}}^3$-ray transition probabilities with the valence space in medium similarity renormalization group ab-initio calculations was performed for the first time in a nucleus far from stability. It was shown that the ab-initio approaches using chiral EFT forces are challenged by detailed high-precision spectroscopic properties of nuclei. The reduced transition probabilities were found to be a very constraining test of the performance of the ab-initio models.

Supplemental Material available