Quantum color transparency and nuclear filtering

Abstract

Color transparency is the proposal that under certain circumstances the strong interactions can be controlled and in some cases reduced in magnitude. We give a comprehensive review of the physics, which hinges on the interface of perturbative QCD with non-perturbative strong interactions. Color transparency is expected to occur in many kinds of quasi-exclusive reactions with either electron or hadron beams. We review the interplay of color transparency with nuclear filtering, which is the conversion of quark wave functions in hadrons to smaller transverse space dimensions by interaction with a nuclear medium. A complete description of these phenomena as a multi-scale QCD process is given in terms of light-cone matrix elements. We also review a number of other approaches, including pictures based on modeling the time evolution of hadronic wave packets and the use of hadronic interpolating states. Spin plays an intrinsic role in hard exclusive reactions and the role of spin in testing and understanding color transparency and nuclear filtering is discussed at length. We emphasize the use of data analysis procedures which have minimal model dependence while comparing and contrasting various models. We review existing experimental data and the experimental program planned at various facilities. We also discuss making use of the subject's strong scientific complementarity and potential for progress in exploring hadron physics at current and future facilities, arguing that the combination of different experiments can lead to a broad new program to study the strong interactions and hadron structure.