Applying new tools to old problems—experimental studies of resonances in 12C

Abstract

We report preliminary results from an experimental study of the p + 11B reaction at beam energies of 2.00 MeV, 2.63 MeV and 3.12 MeV, corresponding to three known 0+, 2+ and 3− resonances in 12C at excitation energies of 17.79 MeV, 18.38 MeV and 18.81 MeV. The resonances have small γ-decay branches to lower-lying resonances of the order of 10−6- 10−5. By detecting the three outgoing a particles in coincidence and measuring their momenta, we obtain complete kinematics information. From the combined energy of the α particles we determine the energy of the γ transition. In this way, we identify two previously observed transitions, (0+, 17.79) → (1+, 12.71) and (3−, 18.38) → (3− 9.64), and one new transition, (2+, 18.81) → (1+, 12.71). The results demonstrate the usefulness of γ decay as a probe of the low-lying resonance spectrum of 12C in the search for new broad (cluster) resonances.