Saturation and parton level Cronin effect: Enhancement versus suppression of gluon production inp−AandA−Acollisions

We note that the phenomenon of perturbative saturation leads to transverse momentum broadening in the spectrum of partons produced in hadronic collisions. This broadening has a simple interpretation as the parton level Cronin effect for systems in which saturation is generated by the “tree level” Glauber-Mueller mechanism. For systems where the broadening results form the nonlinear QCD evolution to high energy, the presence or absence of the Cronin effect depends crucially on the quantitative behavior of the gluon distribution functions at transverse momenta $k_t$ outside the so called scaling window. We discuss the relation of this phenomenon to the recent analysis by Kharzeev, Levin, and McLerran of the momentum and centrality dependence of particle production in nucleus-nucleus collisions at BNL RHIC.