Smooth transition from sudden to adiabatic states in heavy-ion fusion reactions at deep-subbarrier incident energies

We propose a novel extension of the standard coupled-channel (CC) model in order to account for the steep falloff of fusion cross sections at deep-subbarrier incident energies. We introduce a damping factor in the coupling potential in the CC model, simulating smooth transitions from sudden to adiabatic states in deepsubbarrier fusion reactions. The CC model extended with the damping factor can reproduce well not only the steep falloff of the fusion cross section but also the saturation of the logarithmic derivatives for the fusion cross sections at deep-subbarier energies for the 16O+208Pb, 64Ni+64Ni, and 58Ni+58Ni reactions at the deep-subbarrier energies.