Impact Parameter Smearing and Its Influence on Heavy Ion Collision Observables

Based on the Improved Quantum Molecular Dynamics model (ImQMD), the difference of central collision in experiment and theory for low-intermediate energy heavy ion collisions is investigated. By analyzing the two kinds of central collisions, we find there is 50% difference on the charge distribution, and also on its average kinetic energy for heavier fragments, especially at the beam energy of 50 MeV/u. While, for the coalescence invariant neutron proton yield ratio, the calculations show there are about 5% ~ 15% difference. Our results evidence that the impact parameter smearing effects must be considered for tightly constraining the nuclear equation of state and the in-medium nucleon-nucleon cross sections by heavy ion collision.