Sub-barrier enhancement of fusion as compared to a microscopic method inO18+C12

Background: Measurement of the energy dependence of the fusion cross section at sub-barrier energies provides an important test for theoretical models of fusion.Purpose: The aim of the study is to extend the measurement of fusion cross sections in the sub-barrier domain for the $^{18}\mathrm{O}+^{12}\mathrm{C}$ system, and to use the new experimental data to confront microscopic calculations of fusion.Method: Evaporation residues produced in fusion of $^{18}\mathrm{O}$ ions with $^{12}\mathrm{C}$ target nuclei were detected with good geometric efficiency and identified by measuring their energy and time-of-flight. Theoretical calculations with a density-constrained time-dependent Hartree-Fock (DC-TDHF) theory include for the first time the effect of pairing on the fusion cross section.Results: Comparison of the measured fusion excitation function with the predictions of the DC-TDHF calculations reveal that the experimental data exhibit a smaller decrease in cross section with decreasing energy than is theoretically predicted.Conclusion: The larger cross sections observed at the lowest energies measured indicate a larger tunneling probability for the fusion process. This larger probability can be associated with a smaller, narrower fusion barrier than presently included in the theoretical calculations.