The measurement of the giant electric dipole resonance built on the isobaric analog state in the self-conjugate even-even nucleus ${}^{12}\mathrm{C}$ is reported covering a wide excitation energy range. This is done using the ${}^{11}\mathrm{B}$($p,\gamma$) reaction leading to the 15.1 MeV $T=1$ state in ${}^{12}\mathrm{C}$ over a proton energy range of 7 to 24.5 MeV. Two resonances of 1.3 and 2 MeV widths are observed at excitation energies of 24.4 and 28.8 MeV superimposed on a smoothly varying cross section. The γ transitions from both the resonances are assigned $E1$ multipolarity. The structured $T=0$ component of the $E1$ strength distribution is thus very different from that built on the first $T=1$ state in the neighboring nucleus ${}^{14}\mathrm{N}$ and those built on the ground states of ${}^{12}\mathrm{C}$ and ${}^{14}\mathrm{C}$.

• Received 27 December 2007

DOI:https://doi.org/10.1103/PhysRevC.77.051302