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Nuclear shadowing in deep inelastic scattering on nuclei: leading twist versus eikonal approaches

L. Frankfurt, V. Guzey, M. McDermott, M. Strikman

TL;DR

This work contrasts leading twist QCD and eikonal approaches to nuclear shadowing in deep inelastic scattering on nuclei, highlighting how Gribov-inspired diffraction connects shadowing to diffractive parton distributions measured at HERA. The LT framework, which includes QCD evolution via DGLAP and diffractive input f_{j/N}^{D}, predicts sizable shadowing for both sea quarks and gluons and a distinct, slower Q^2 dependence; the eikonal approach, treating the interaction as a frozen dipole series, generally underestimates shadowing at higher Q^2 and cannot accommodate gluon-driven effects or proper QCD evolution. A key finding is the dramatic difference in predictions for the longitudinal structure function F_L^A, with LT yielding much larger shadowing than the eikonal model, offering a powerful observable to distinguish the two pictures. Central collisions amplify shadowing, while centrality-dependent measurements and future F_L^A data could provide decisive tests of the underlying space-time dynamics and diffractive structure in nuclei.

Abstract

We use several diverse parameterizations of diffractive parton distributions, extracted in leading twist QCD analyses of the HERA diffractive deep inelastic scattering (DIS) data, to make predictions for leading twist nuclear shadowing of nuclear quark and gluon distributions in DIS on nuclei. We find that the HERA diffractive data are sufficiently precise to allow us to predict large nuclear shadowing for gluons and quarks, unambiguously. We performed detailed studies of nuclear shadowing for up and charm sea quarks and gluons within several scenarios of shadowing and diffractive slopes, as well as at central impact parameters. We compare these leading twist results with those obtained from the eikonal approach to nuclear shadowing (which is based on a very different space-time picture) and observe sharply contrasting predictions for the size and Q^2-dependence of nuclear shadowing. The most striking differences arise for the interaction of small dipoles with nuclei, in particular for the longitudinal structure function F_{L}^{A}.

Nuclear shadowing in deep inelastic scattering on nuclei: leading twist versus eikonal approaches

TL;DR

This work contrasts leading twist QCD and eikonal approaches to nuclear shadowing in deep inelastic scattering on nuclei, highlighting how Gribov-inspired diffraction connects shadowing to diffractive parton distributions measured at HERA. The LT framework, which includes QCD evolution via DGLAP and diffractive input f_{j/N}^{D}, predicts sizable shadowing for both sea quarks and gluons and a distinct, slower Q^2 dependence; the eikonal approach, treating the interaction as a frozen dipole series, generally underestimates shadowing at higher Q^2 and cannot accommodate gluon-driven effects or proper QCD evolution. A key finding is the dramatic difference in predictions for the longitudinal structure function F_L^A, with LT yielding much larger shadowing than the eikonal model, offering a powerful observable to distinguish the two pictures. Central collisions amplify shadowing, while centrality-dependent measurements and future F_L^A data could provide decisive tests of the underlying space-time dynamics and diffractive structure in nuclei.

Abstract

We use several diverse parameterizations of diffractive parton distributions, extracted in leading twist QCD analyses of the HERA diffractive deep inelastic scattering (DIS) data, to make predictions for leading twist nuclear shadowing of nuclear quark and gluon distributions in DIS on nuclei. We find that the HERA diffractive data are sufficiently precise to allow us to predict large nuclear shadowing for gluons and quarks, unambiguously. We performed detailed studies of nuclear shadowing for up and charm sea quarks and gluons within several scenarios of shadowing and diffractive slopes, as well as at central impact parameters. We compare these leading twist results with those obtained from the eikonal approach to nuclear shadowing (which is based on a very different space-time picture) and observe sharply contrasting predictions for the size and Q^2-dependence of nuclear shadowing. The most striking differences arise for the interaction of small dipoles with nuclei, in particular for the longitudinal structure function F_{L}^{A}.

Paper Structure

This paper contains 13 sections, 41 equations.

Table of Contents

  1. Introduction
  2. The leading twist and eikonal approaches to nuclear shadowing
  3. The leading twist approach
  4. The master formulae for leading twist nuclear shadowing
  5. The transition between shadowing and antishadowing: setting $x_{I\!\!P, 0}$.
  6. Numerical predictions for nuclear PDFs and $F_2^A$
  7. Predictions for central collisions
  8. The eikonal approximation approach
  9. Differences between the leading twist and eikonal approaches
  10. Nuclear shadowing of the longitudinal structure function $F_{L}^{A}$
  11. Conclusions and discussion
  12. Parameterizations of diffractive parton distributions and $\sigma_{eff}$
  13. Parameterization of the nuclear one-body density