Production and Thermal Equilibration of Partons in Relativistic Heavy Ion Collisions: sqrt{s}= 20 vs. 200 A GeV

The production and thermalization of partons liberated in relativistic heavy ioncollisions is investigated within the parton cascade model. The momentum distribution of the partons near z=0 is found to become isotropic beyond about 1 fm/c after the overlap for the collision of lead nuclei at $\sqrt{s}=20 A GeV$ indicating a thermalization. At $\sqrt{s}=200 A GeV$ this is attained by about 0.5 fm/c after the complete overlap.