Diffractive Phenomena in High Energy Processes

Abstract

We review the evolution of the studies of diffractive processes in the strong interaction over the last 60 years. First, we briefly outline the early developments of the theory based on analyticity and unitarity of the S-matrix, including the derivation and exploration of the Regge trajectories and related moving cuts. Special attention is paid to the concept of the Pomeron trajectory introduced for description of total, elastic and diffractive cross sections at high energies and to the emergence of the dynamics of multi-Pomeron interactions. The role of large longitudinal distances and color coherent phenomena for the understanding of inelastic diffraction in hadron-hadron scattering and deep inelastic scattering is emphasized. The connection of these phenomena to the cancellation of the contribution of the Glauber approximation in hadron-nucleus collisions and to the understanding of the Gribov-Glauber approximation is explained. The presence of different scales in perturbative QCD due to masses of heavy quarks has led to the emergence of numerous new phenomena including nonuniversality of the slopes of Regge trajectories made of light and heavy quarks and non-universal energy dependence of elastic cross sections. The application of the perturbative QCD techniques allowed us to calculate from the first principles the interaction of small transverse 1 arXiv:1304.4308v1 [hep-ph] 16 Apr 2013 size color singlets with hadrons leading to the development of the quantitative theory of hard exclusive reactions and to the successful prediction of many regularities in hard large mass diffraction. It also led to the prediction of the phenomenon of complete transparency of nuclear matter in QCD in special processes. The conflict of perturbative QCD with probability conservation for high energy processes of virtual photon-nucleon scattering is explained. Some properties of the new QCD regime are outlined.

Taming of preasymptotic small x evolution within resummation framework

“…A related effect was observed in QED in the process of production of e + e − pairs by Lipatov and Kuraev [14]. For further discussion, see [15]. This results in NLL corrections being very large and negative.…”

Global analysis of color fluctuation effects in proton– and deuteron–nucleus collisions at RHIC and the LHC

“…Thus certain physical properties of the parton system of a rapidly moving hadron, such as the total transverse area occupied by the color fields, may change collision by collision, a phenomenon we refer to as color fluctuations [1,2]. These variations in the internal structure of hadrons have a wide range of observable consequences, such as inelastic diffraction [3][4][5]. In quantum chromodynamics (QCD), the configurations in which a large (> 10%) fraction of the hadron's momentum is carried by a single parton are spatially compact.…”