NuHamil : A numerical code to generate nuclear two- and three-body matrix elements from chiral effective field theory

Impact of Two-Body Currents on Magnetic Dipole Moments of Nuclei

We investigate the effects of two-body currents on magnetic dipole moments of medium-mass and heavy nuclei using the valence-space in-medium similarity renormalization group with chiral effective field theory interactions and currents. Focusing on near doubly magic nuclei from oxygen to bismuth, we have found that the leading two-body currents globally improve the agreement with experimental magnetic moments. Moreover, our results show the importance of multishell effects for ^{41}Ca, which suggest that the Z=N=20 gap in ^{40}Ca is not as robust as in ^{48}Ca. The increasing contribution of two-body currents in heavier systems is explained by the operator structure of the center-of-mass dependent Sachs term.

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

The excited states of unstable ^{20}O were investigated via γ-ray spectroscopy following the ^{19}O(d,p)^{20}O reaction at 8  AMeV. By exploiting the Doppler shift attenuation method, the lifetimes of the 2_{2}^{+} and 3_{1}^{+} states were firmly established. From the γ-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 γ-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.