Reduction of the fusion cross-section in ¹⁹O + ¹²C at above-barrier energies

Near-barrier fusion excitation functions were measured for ^19,20O + ¹²C and ¹⁹F + ¹²C using the active-target MuSIC@Indiana detector at the GANIL accelerator facility. Comparison with an independent measurement of ¹⁹O + ¹²C confirms the existence of a large (~180 mb) suppression of fusion at E_c.m.~ 12 MeV. This suppression is not observed for the fusion of ^18,20O with ¹²C. Although time-dependent Hartree-Fock calculations, which include ℓ-wave dependent barriers, describe the fusion cross-section at low energies (E_c.m.< 10 MeV), they overpredict the cross-section at higher energies. Coupled-channels calculations provide a reasonable description of the cross-section over the entire energy range measured, but slightly underpredict the cross-section at low energies for ¹⁹O and ²⁰O. Both theoretical models fail to describe the main feature of the ¹⁹O excitation function, namely the significant suppression observed at E_c.m.~ 12 MeV. This suppression in ¹⁹O suggests the opening of a new reaction channel, above a minimum energy and angular momentum threshold that does not lead to fusion.