Influence of complex surface vibrations on the fusion of 58Ni+60Ni

Fusion-evaporation cross sections for 58Ni+60Ni have been measured with high accuracy in the energy range around the Coulomb barrier. The data yield an ''experimental distribution of fusion barriers'' around 13 MeV wide, which displays structure characteristic of strong phonon couplings with two large well ''resolved'' peaks, and a smaller peak at lower energies, which is essential for fitting the low-energy cross section. This is obtained only when the target and projectile double-phonon excitations are taken into account. This is the first time that such complex surface vibrations have been identified in a fusion experiment