Cluster Thomas-Ehrman effect in mirror nuclei

The Coulomb shift is analyzed for the mirror cluster systems of ${}^{18}\mathrm{O}=\alpha +{}^{14}\mathrm{C}$ and ${}^{18}\mathrm{Ne}=\alpha +{}^{14}\mathrm{O}$ by applying the orthogonality condition model (OCM). The OCM calculation clearly predicts the suppressed excitation energy of the higher $0^{+}$ states in the proton-rich system of ${}^{18}\mathrm{Ne}$. This results can be interpreted in terms of the extension of the Thomas-Ehrman shift (TES), which is discussed in ${}^{17}\mathrm{O}={}^{16}\mathrm{O}+N$ and ${}^{17}\mathrm{F}={}^{16}\mathrm{O}+P$, to the cluster degrees of freedom. A combination of the cluster TES and the monopole transition is proposed as an experimental probe to identify the cluster structure in mirror systems.

Figure 1

Energy spectra in ${}^{18}\mathrm{O}=\alpha +{}^{14}\mathrm{C}$. The left and right levels are the results of the theoretical calculation and the experimental observations, respectively. The dashed line shows the $\alpha$ threshold, whereas the shades attached to the resonant levels represent the decay width.

Figure 2

Excitation scheme of $0^{+}$ levels in $\alpha +{}^{14}\mathrm{C}$. The horizontal dashed line shows the $\alpha$ threshold. The number attached to the individual levels means the population of the dominant channel component. The dotted arrows with the boxes represent the excitation schemes, such as the cluster relative excitation (Cl. Ex.) and the rearrangement (Rearrange.). See the text for details.