IsovectorM2state observed in theC14(π−, γ)reaction

The photon spectrum of the pion capture reaction ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}({\pi }^{-}, \gamma ){}_{}{}^{14}{}_{}{}^{}\mathrm{B}$ was measured with a resolution of 0.9 MeV full width at half maximum. A single strong transition is observed with $\gamma$-ray energy 115.70±0.17 MeV, corresponding to a state in ${}_{}{}^{14}{}_{}{}^{}\mathrm{B}$ at 2.15±0.17-MeV excitation. Comparisons with previous experiments and theoretical calculations identify this as the second $T=2, 2^{-}$ state in mass-14 nuclei. The single strong transition has a measured branching ratio (11.1±3.0)×${10}^{-4\mathrm{}}$, which equals one-fifth of the shell-model prediction. The total radiative capture branching ratio is 0.68±0.16%, which is a factor of 2 to 3 smaller than for other 1-$p$-shell nuclei.