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Diffraction in Deep Inelastic Scattering

A. Hebecker

TL;DR

Diffraction in Deep Inelastic Scattering analyzes how diffractive events at small $x$ arise from color-singlet exchange between a virtual photon's partonic fluctuations and the proton's color field. It develops and contrasts several frameworks, notably the semiclassical approach tied to diffractive parton distributions, soft pomeron ideas, and perturbative two-gluon exchange, and connects them through target-rest-frame and Breit-frame perspectives. The work shows that leading-twist diffraction is captured by diffractive parton distributions and non-forward gluon distributions, while nonperturbative color dynamics and higher-twist effects shape many observables, with factorization theorems underpinning the hard-soft separation. It surveys color-field models (large targets, stochastic vacuum, and dipole formalisms), and tests them against HERA data on $F_2^D$ and final states (jets, charm, vector mesons), while highlighting open issues such as the energy dependence and the precise balance between soft and hard color-singlet exchange in diffractive processes.

Abstract

Different theoretical methods used for the description of diffractive processes in small-x deep inelastic scattering are reviewed. The semiclassical approach, where a partonic fluctuation of the incoming virtual photon scatters off a superposition of target colour fields, is used to explain the basic physical effects. In this approach, diffraction occurs if the emerging partonic state is in a colour singlet, thus fragmenting independently of the target. Other approaches, such as the idea of the pomeron structure function and two gluon exchange calculations, are also discussed in some detail. Particular attention is paid to the close relation between the semiclassical approach and the method of diffractive parton distributions, which is linked to the relation between the target rest frame and the Breit frame point of view. While the main focus is on diffractive structure functions, basic issues in the diffractive production of mesons and of other less inclusive final states are also discussed. Models of the proton colour field, which can be converted into predictions for diffractive cross sections using the semiclassical approach, are presented. The concluding overview of recent experimental results is very brief and mainly serves to illustrate implications of the theoretical methods presented.

Diffraction in Deep Inelastic Scattering

TL;DR

Diffraction in Deep Inelastic Scattering analyzes how diffractive events at small arise from color-singlet exchange between a virtual photon's partonic fluctuations and the proton's color field. It develops and contrasts several frameworks, notably the semiclassical approach tied to diffractive parton distributions, soft pomeron ideas, and perturbative two-gluon exchange, and connects them through target-rest-frame and Breit-frame perspectives. The work shows that leading-twist diffraction is captured by diffractive parton distributions and non-forward gluon distributions, while nonperturbative color dynamics and higher-twist effects shape many observables, with factorization theorems underpinning the hard-soft separation. It surveys color-field models (large targets, stochastic vacuum, and dipole formalisms), and tests them against HERA data on and final states (jets, charm, vector mesons), while highlighting open issues such as the energy dependence and the precise balance between soft and hard color-singlet exchange in diffractive processes.

Abstract

Different theoretical methods used for the description of diffractive processes in small-x deep inelastic scattering are reviewed. The semiclassical approach, where a partonic fluctuation of the incoming virtual photon scatters off a superposition of target colour fields, is used to explain the basic physical effects. In this approach, diffraction occurs if the emerging partonic state is in a colour singlet, thus fragmenting independently of the target. Other approaches, such as the idea of the pomeron structure function and two gluon exchange calculations, are also discussed in some detail. Particular attention is paid to the close relation between the semiclassical approach and the method of diffractive parton distributions, which is linked to the relation between the target rest frame and the Breit frame point of view. While the main focus is on diffractive structure functions, basic issues in the diffractive production of mesons and of other less inclusive final states are also discussed. Models of the proton colour field, which can be converted into predictions for diffractive cross sections using the semiclassical approach, are presented. The concluding overview of recent experimental results is very brief and mainly serves to illustrate implications of the theoretical methods presented.

Paper Structure

This paper contains 24 sections, 270 equations, 45 figures.

Table of Contents

  1. Preface
  2. Models for diffraction
  3. The semiclassical method and its relation to other approaches
  4. Kinematics
  5. Fundamental observations
  6. Diffractive structure function
  7. Eikonal formulae for high-energy scattering
  8. Production of $q\bar{q}$ pairs
  9. Higher Fock states
  10. Field averaging
  11. Soft pomeron
  12. Pomeron structure function
  13. Diffractive parton distributions
  14. Target rest frame point of view
  15. Elastic meson production
  16. ...and 9 more sections

Figures (45)

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  • ...and 40 more figures