QCD Factorization and Re-scattering in Proton-Nucleus Collisions

The extension of the factorization theorems of perturbative QCD to power corrections associated with re-scattering in nuclear collisions is reviewed. The importance of hadron-nucleus collisions is discussed. Perturbative QCD (pQCD) has been very successful in interpreting and predicting hadronic scattering processes in high energy collisions, even though the physics associated with individual hadron’s wave function is nonperturbative. It is the QCD factorization theorem [1] that provides prescriptions to separate longfrom short-distance effects in hadronic cross sections. The leading power contributions to a general hadronic cross section involve only one hard collision between two partons from two incoming hadrons of momenta pA and pB. The momentum scale of the hard collision is set by producing either a heavy particle (like W/Z or virtual photon in Drell-Yan production) or an energetic third parton, which fragments into either a jet or a hadron h of momentum p. The cross section can be factorized as [1] Eh dσAB→h(p′) d3p′ = ∑