High p_T hadron spectra in high-energy heavy-ion collisions

We calculate the hadron spectra in high-energy pp, pA and AA collisions within a pQCD parton model. Analyses of experimental data show that the modification of the spectra in pA and AA as compared to that in $pp$ collisions is consistent with multiple parton scattering scenario and is dictated by the transition from absorptive soft interaction at low p_T to incoherent hard parton scattering at high p_T. This analysis not only sheds new light on the limits to the physics analysis based on thermal fire-ball models but also provides a more quantitative baseline results on which one can study the effects of parton energy loss in the hadron spectra at high p_T.