Quark pair production in high energy pA collisions: General features

A consistent treatment of both multiple scattering and small x quantum evolution effects on pair production in high energy pA collisions is feasible in the framework of the color glass condensate (CGC) [J.P. Blaizot, F. Gelis, R. Venugopalan, Nucl. Phys. A 743 (2004) 57]. We first discuss the properties of quark pair production in the classical effective theory where only multiple scattering effects are included. Explicit results are given for pair production as a function of the invariant mass of pairs, the pair momenta, the atomic mass number A and the quark mass. We relate the logarithms that appear in our formulation of pair production to logarithms that appear in the limit of collinear factorization in QCD. Violations of k⊥ factorization and medium modifications, as represented by the Cronin effect, are also investigated. We next consider how small x quantum evolution (shadowing) effects modify the results for pair production. In particular, we provide results for the rapidity distribution of pairs and the dependence of the Cronin effect on rapidity. We discuss the dependence of our results on the initial conditions for small x evolution and comment on its implications for pair production at RHIC and the LHC.