Space-time structure of initial parton production in ultrarelativistic heavy ion collisions

The space and time evolution of initial parton production in ultrarelativistic heavy ion collisions is investigated within the framework of perturbative QCD which includes both initial and final state radiations. The uncertainty principle is used to relate the lifetime of a radiating parton to its virtuality and momentum. The interaction time of each hard or semihard parton scattering is also taken into account. For central Au+Au collisions at $\sqrt{s}=200\mathrm{}$ GeV, most of the partons are found to be produced within 0.5 fm/c after the total overlap of the two colliding nuclei. The local momentum distribution is approximately isotropical at that time. The implication on how to treat correctly the secondary scattering in an ultimate parton cascading model is also discussed.