  In this talk we present a perturbative QCD improved parton model calculation
for light meson production in high energy heavy ion collisions. In order to
describe the experimental data properly, one needs to augment the standard pQCD
model by the transverse momentum distribution of partons ("intrinsic k_T").
Proton-nucleus data indicate the presence of nuclear shadowing and
multiscattering effects. Further corrections are needed in nucleus-nucleus
collisions to explain the observed reduction of the cross section. We introduce
the idea of proton dissociation and compare our calculations with the SPS and
RHIC experimental data.
