High-Precision Spectroscopy of 20O Benchmarking Ab Initio Calculations in Light Nuclei

Abstract

The excited states of unstable 20O were investigated via -ray spectroscopy following the 19O⁡( , )⁢20O reaction at 8 ⁢MeV. By exploiting the Doppler shift attenuation method, the lifetimes of the 2+2 and 3+1 states were firmly established. From the -ray branching and ⁢2/ ⁢1 mixing ratios for transitions deexciting the 2+2 and 3+1 states, the ⁡( ⁢2) and ⁡( ⁢1) 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 -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 effective field theory 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.