Elimination of fast variables and initial slip: a new mechanism for fusion hindrance in heavy-ion collisions

Synthesis of superheavy elements by fusion-evaporation reactions is limited by extremely low cross-sections. One of the reasons for the reduced cross-sections is the so-called quasifission, which hinders fusion for reactions with heavy systems. It is widely acknowledged that fusion hindrance is due to a conditional saddle that has yet to be overcome in a dissipative environment, in order to reach the compound configuration from the contact point. However, the dynamical description is not yet well established. In this communication we show that elimination of fast variables to reduce the number of degrees of freedom leads to a slip of the initial conditions of the slow variables, which has a significant impact on the amplitude of the hindrance phenomenon. The energy dependence of the slip is similar to the phenomenological shift introduced in the 'fusion by diffusion' model.