Mirror-symmetry structure ofA=27,T=1/2nuclei studied through strong, weak, and electromagnetic interactions
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Abstract
Gamow-Teller (GT) transitions and $M1$ transitions from or to the ground states are analogous in the pair of $T=1/2$ mirror nuclei, if the excited states hold the mirror-symmetry properties. In order to study the mirror-symmetry structure of the $A=27$ mirror nuclei ${}^{27}\mathrm{Al}$ and ${}^{27}\mathrm{Si},$ experimental data on GT transition strengths obtained from ${}^{27}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{Si}}}^{27}\mathrm{Al}$ $\ensuremath{\beta}$ decay and from a good-resolution ${}^{27}\mathrm{Al}{(}^{3}\mathrm{He}{,t)}^{27}\mathrm{Si}$ reaction at 150 MeV/nucleon and 0\ifmmode^\circ\else\textdegree\fi{} have been compared with $M1$ transition strengths obtained from $\ensuremath{\gamma}$ decay in ${}^{27}\mathrm{Al}$ and ${}^{27}\mathrm{Al}(\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}})$ reaction. Good overall correspondence of transitions is observed for states up to nearly 9 MeV in excitation energy, where the particle-decay channel becomes important. The difference of excitation energies of analog states in the mirror nuclei are about 250 keV at this excitation energy. From a comparison of $B(M1)$ and $B(\mathrm{GT})$ strengths of the analogous transitions, the contribution of the isoscalar and the orbital terms in the $M1$ operator is found to become prominent in weak $M1$ transitions.