Hadronic Diffraction: Where do we Stand?

TL;DR

This paper reviews experimental data on hadronic diffraction, highlighting how diffractive processes can be understood through a QCD-based partonic picture involving low-x partons and rapidity gaps.

Contribution

It presents a unified framework for understanding both soft and hard diffraction using factorization and parton distribution functions within QCD.

Findings

Diffractive cross sections factorize into total cross section and gap formation probability.

Normalizing gap probability yields consistent cross sections for various diffraction types.

Diffraction is mediated by low-x partons under color constraints.

Abstract

Experimental results on hadronic soft and hard diffractive processes are reviewed with emphasis on aspects of the data that point to the underlying QCD mechanism for diffraction. Diffractive differential cross sections are shown to be factorized into two terms, one representing the total cross section at the reduced energy, corresponding to the rapidity region(s) in which there is particle production, and another interpreted as the probability of formation of the rapidity gap(s) characterizing diffraction. By (re)normalizing the term of gap formation probability to unity, cross sections for single, central, and multiple rapidity gap soft diffraction, as well as structure functions for hard diffraction processes, are obtained from the underlying inclusive parton distribution functions. A unified partonic picture emerges, in which diffraction appears to be mediated by the exchange of low-x partons subject to color constraints.