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

TL;DR

This study combines high-precision gamma-ray spectroscopy of unstable $^{20}$O with comparisons to advanced ab-initio nuclear models, revealing challenges in current theoretical approaches for describing detailed nuclear properties.

Contribution

It provides the first detailed comparison of experimental gamma-ray transition data with valence space ab-initio calculations using chiral EFT forces in a nucleus far from stability.

Findings

Ab-initio models struggle to accurately predict high-precision spectroscopic data.

Transition probabilities serve as a stringent test for nuclear theory.

Experimental data challenges existing chiral EFT Hamiltonians.

Abstract

The excited states of unstable $^{20}$O were investigated via $\gamma$-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 $\gamma$-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 $\gamma$-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.