Abstract
We study nuclear effects in production of Drell-Yan pairs and direct photons in proton-nucleus collisions. For the first time, these effects are studied within the color dipole approach using the Green function formalism which naturally incorporates the color transparency and quantum coherence effects. The corresponding numerical results for the nuclear modification factor are compared with available data. Besides, we present a variety of predictions for the nuclear suppression as a function of transverse momentum pT, Feynman variable xF and invariant mass M of the lepton pair which can be verified by experiments at RHIC and LHC. We found that the nuclear suppression is caused predominantly by effects of quantum coherence (shadowing corrections) and by the effective energy loss induced by multiple initial state interactions. Whereas the former dominate at small Bjorken x2 in the target, the latter turns out to be significant at large x1 in the projectile beam and is universal at different energies and transverse momenta. (Less)
Highlights
The color dipole approach [1] represents a phenomenological framework that effectively takes into account the higher-order and nonlinear QCD effects
We found that the nuclear suppression is caused predominantly by effects of quantum coherence and by the effective energy loss induced by multiple initial state interactions
We include the gluon shadowing (GS) that dominates at small Bjorken x2 and the effective energy loss induced by multiple initial state interactions
Summary
The color dipole approach [1] represents a phenomenological framework that effectively takes into account the higher-order and nonlinear QCD effects. There are many studies in the literature demonstrating a reliable agreement of predictions with experimental data, especially at high energies and/or small Bjorken variable x2 in proton-proton (pp) collisions and DIS Accounts for the exact coherence length lc and naturally incorporates the color transparency and quantum coherence effects. Such a kinematic region corresponds e.g. to kinematics at RHIC fixed target experiments or planned experiments such as AFTER@LHC. We include the gluon shadowing (GS) that dominates at small Bjorken x2 and the effective energy loss induced by multiple initial state interactions
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