Effects of Surface Emitting and Cumulative Collisions on Elliptic Flow

The integral and differential elliptic flow of partons is calculated using the multiphase transport model for Au+Au collisions at centre-of-mass energy
√s_NN=200GeV. It is shown that elliptic flow of partons freezing out at early time, which is affected mainly by surface emittance, decreases with time and elliptic flow of partons freezing out at late time, which is dominated by cumulative collisions, increases with time. The elliptic flow of partons freezing out early has a large contribution to the flatting of curve of final differential elliptic flow at large transverse momentum. It is argued that the effect of surface emittance is not neglectable.