Eccentricity and elliptic flow at a fixed centrality in Au+Au collisions at in an AMPT model

Abstract

In this paper, elliptic flow is studied at a fixed centrality in Au+Au collisions at in the AMPT model. It is observed that as the participants increase, elliptic flow either increases or decreases at a different fixed impact parameter, but it does not have a trivial fluctuation. It is analyzed that the initial space anisotropy dominates the participant dependence of elliptic flow in near-central collisions(b = 5 fm) and mid-central collisions(b = 8 fm), while the interaction between particles can mainly answer for the elliptic flow behavior with the participant in peripheral collisions (b = 12 fm). To distinguish the pure geometrical effect, elliptic flow scaled by initial eccentricity is studied. It is found that the ratio ν2/∊ increases with the participant and reaches a saturation when the participant is large enough, indicating that the collision system may reach a local equilibrium.