A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the $\beta$ decay of the $A=14$ multiplet is presented. The GT strength distributions to excited states in ${}^{14}\mathrm{C}$ and ${}^{14}\mathrm{O}$ were studied in high-resolution $(d,{}^2\mathrm{He})$ and $({}^3\mathrm{He},t)$ charge-exchange reactions on ${}^{14}\mathrm{N}$. No-core shell-model calculations capable of reproducing the suppression of the $\beta$ decays predict a selective excitation of $J^{\pi }=2^{+}$ states. The experimental confirmation represents a validation of the assumptions about the underlying structure of the ${}^{14}\mathrm{N}$ ground state wave function. However, the fragmentation of the GT strength over three $2^{+}$ final states remains a fundamental issue not explained by the present no-core shell model using a $6\hslash \omega$ model space, suggesting possibly the need to include cluster structure in these light nuclei in a consistent way.

• Received 7 April 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.062502