Intruder-driven mirror energy differences between ${}^{29}$Cl and ${}^{29}$Mg studied with antisymmetrized molecular dynamics

Abstract

To clarify the mirror energy differences (MEDs) of the proton-unbound nucleus ${}^{29}$Cl and their microscopic origins, we investigate the low-lying states of the ${}^{29}$Cl-${}^{29}$Mg mirror pair using antisymmetrized molecular dynamics. The calculation reasonably reproduces the normal and intruder states of ${}^{29}$Mg, while suggesting alternative spin-parity assignments for ${}^{29}$Cl. The $1/2^{+}$ and $3/2^{+}$ states are predicted to form a nearly degenerate ground-state doublet with a small MED because of their similar intrinsic structures. In contrast, the $3/2^{-}$ and $7/2^{-}$ intruder states exhibit large negative MEDs and are assigned to the observed resonances at approximately 500~keV and 1.1~MeV, respectively. Their large MEDs originate from the reduced Coulomb energies associated with the stronger deformation and spatially extended proton distributions in the intruder configurations.

Comments: 6 pages, 3 figures