Structure evolution of ground and excited states in the exotic nucleus ${}^{22}$Al

Abstract

Recent experimental studies on proton-rich nuclei in the $sd$ shell have revealed intriguing near-threshold phenomena, including exotic structures associated with mirror-symmetry breaking. In particular, a halo-like structure has been suggested for the $1^{+}$ state of ${}^{22}$Al based on the large isospin asymmetry observed in the ${}^{22}$Si/${}^{22}$O mirror Gamow-Teller transitions. Recent mass measurements further indicate that the ground state of ${}^{22}$Al is weakly bound, with a single-proton separation energy of about 100 keV. To investigate how the continuum affects the structure and decay properties of this proton-dripline nucleus, we employ the state-of-the-art Gamow shell model. This approach utilizes valence-space effective interactions and operators derived from chiral forces. Our calculations identify the ground state of ${}^{22}$Al as a $4^{+}$ state, with a $3^{+}$ state as the first excitation. Despite their diffuse nature under weak binding, the Thomas-Ehrman shift for these states is found to be negligible due to their small $s$-wave components. In contrast, the excited $1_1^{+}$ state possesses a significantly larger $s$-wave component, resulting in a more pronounced halo-like structure.

8 pages, 2 figures, 3 tables