Cold nuclear matter effects in p+A reactions and their application to Fermilab, RHIC and LHC experiments

Proton-nucleus (p+A) collisions have long been recognized as a critical component of the relativistic heavy ion program. It provides the baseline measurements for nucleus-nucleus collisions and serves as a powerful probe of the properties of dense QCD matter. The nontrivial QCD dynamics in p+A reactions is usually referred to as cold nuclear matter (CNM) effects, which include cold nuclear matter energy loss, Cronin effect and nuclear shadowing. In this talk, I will first show how to compute the parton energy loss effect in large nuclei in perturbative QCD by considering the Drell-Yan process in p+A collisions. It turns out that the medium induced radiative energy loss due to multiple scattering leads to the suppression of the Drell-Yan cross section in p + A relative to p + p collisions. Our numerical results are consistent with the Fermilab experimental data. All other CNM effects are also centered around the idea of multiple parton scattering. We explain how to incorporate these effects within the pQCD formalism, and present results and predictions for the nuclear modification of inclusive light hadron and prompt photon production at RHIC and LHC, respectively. We find that this theoretical approach can describe the RHIC d+Au data rather well. The LHC p+Pb predictions will soon be confronted by new experimental results and will help clarify the magnitude and origin of CNM effects and facilitate precision dense QCD matter tomography.