The Mechanism of the Anomalous Energy Shift between s-States in Mirror Nuclei with a Halo Structure

A mechanism of the anomalous energy shift between s-states in mirror nuclei is investi gated by using the complex scaling method (CSM). The s-states are described by a resonant core+p system and by a loosely bound core+n system, where the latter reproduces a neu tron halo structure. To understand the mechanism of the anomalous energy shift appearing in the resonant s-state of the core+p system, we pick out the complex expectation values of the Coulomb potential and kinetic energy operators from the Hamiltonian for resonant states, using the procedure recently developed in the framework of the CSM. We find that the kinetic energy reduction is large, in addition to the Coulomb energy reduction in the ordinary Thomas-Ehrman shift. As a result, a large energy shift is reasonably explained by the combination of two mechanisms of the kinetic energy reduction and the Coulomb energy reduction.