Ground-state mass of 22Al and test of state-of-the-art ab initio calculations

The ground-state mass excess of the Tz = −2 drip-line nucleus 22Al is measured for the first time to be 18103(10) keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou. The new mass excess value allowed us to determine the excitation energies of the two low-lying 1+ states in 22Al with significantly reduced uncertainties of 51 keV. Comparing to the analogue states in its mirror nucleus 22F, the mirror energy differences of the two 1+ states in the 22Al-22F mirror pair are determined to be −625(51) keV and −330(51) keV, respectively. The excitation energies and the mirror energy differences are used to test the state-of-the-art ab initio valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory. The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of the πs1/2 orbital.