Adiabatic quantum tunneling in heavy-ion sub-barrier fusion

High precision measurements of the fusion excitation functions for the reactions Ca + Pt, Os clearly demonstrate that projectile excitation significantly modifies the potential barrier distribution. In sharp contrast, fusion of O + Sm appears to show no influence of the projectile excitation on the shape of the barrier distribution. These apparently conflicting conclusions are reconciled in this work, using realistic coupled– channels calculations, which show that high energy states produce an adiabatic potential renormalisation. This result indicates that adiabatic effects restrict, in a natural way, the states which influence the shape of a fusion barrier distribution. The analysis of barrier distributions thus offers a criterion for the relevance of the ‘counter term’ prescription in the Caldeira-Leggett approach. PACS numbers: 25.70.Jj, 24.10.Eq, 21.60.Ev, 27.60.+n