Precision mass measurements of magnesium isotopes and implications on the validity of the Isobaric Mass Multiplet Equation

TL;DR

This study measured magnesium isotopes' masses with high precision to test the Isobaric Mass Multiplet Equation, finding a significant cubic deviation that suggests potential new physics or experimental errors.

Contribution

It provides the most precise magnesium isotope mass measurements and identifies the largest known cubic coefficient in the IMME, challenging current theoretical models.

Findings

Identified a cubic coefficient of 28(7) keV in the IMME.

Measured magnesium isotope masses with up to 34 times higher precision.

Found good agreement between experimental results and ab initio calculations.

Abstract

If the mass excess of neutron-deficient nuclei and their neutron-rich mirror partners are both known, it can be shown that deviations of the Isobaric Mass Multiplet Equation (IMME) in the form of a cubic term can be probed. Such a cubic term was probed by using the atomic mass of neutron-rich magnesium isotopes measured using the TITAN Penning trap and the recently measured proton-separation energies of $^{29}$Cl and $^{30}$Ar. The atomic mass of $^{27}$Mg was found to be within 1.6$\sigma$ of the value stated in the Atomic Mass Evaluation. The atomic masses of $^{28,29}$Mg were measured to be both within 1$\sigma$, while being 8 and 34 times more precise, respectively. Using the $^{29}$Mg mass excess and previous measurements of $^{29}$Cl we uncovered a cubic coefficient of $d$ = 28(7) keV, which is the largest known cubic coefficient of the IMME. This departure, however, could also be caused by experimental data with unknown systematic errors. Hence there is a need to confirm the mass excess of $^{28}$S and the one-neutron separation energy of $^{29}$Cl, which have both come from a single measurement. Finally, our results were compared to ab initio calculations from the valence-space in-medium similarity renormalization group, resulting in a good agreement.