Sub-barrier fusion ofCa40+Zr94: Interplay of phonon and transfer couplings

A precise fusion excitation function has been measured for 40 Ca+ 94 Zr at near- and sub-barrier energies, and the fusion barrier distribution has been extracted. Comparing with the existing data for 40,48 Ca+ 90,96 Zr shows that couplings to inelastic excitations determine the fusion cross sections and the shape of the barrier distributions near the barrier. At lower energies, the two systems possessing neutron-transfer channels with large positive Q-values ( 40 Ca+ 94,96 Zr) have remarkably similar cross sections, and both show a large enhancement with respect to the other systems and to coupled-channels calculations including up to three quadrupole and octupole phonons in the Zr targets.