Perturbative QCD Results on Pion Production in pp, pA and AA Collisions

We summarize new pQCD results on pion production in proton-proton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our calculation introduces intrinsic parton transverse momentum (k T ) and is performed effectively at next-to-leading order (NLO), applying a K factor extracted for jet events. Two different factorization scales, Q = p T, jet /2 and p T, jet are used. Experimental data in pA collisions imply a preference for the latter choice at NLO level. We display our results at CERN SPS for AA collisions.