The ground-state mass excess of the Tzβ=β2 drip-line nucleus 22Al is
measured for the first time to be 18103(10) keV using the newly-developed
BΟ-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 β625(51) keV and
β330(51) keV, respectively. The excitation energies and the mirror energy
differences are used to test the state-of-the-art \textit{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 Οs1/2β orbital.Comment: 8 pages, 5 figure