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Scaling properties of nuclear parton distributions in short-range-correlation motivated two-component parametrization

Petja Paakkinen

TL;DR

This work scrutinizes a short-range correlation (SRC) motivated two-component parametrization of nuclear parton distribution functions (nPDFs). It shows a rescaling invariance prevents unique determination of the global SRC abundance normalizations, so only ratios C^A_p/C^{A_ref}_p and C^A_n/C^{A_ref}_n are physically meaningful; it offers a reformulated parametrization that avoids this issue by focusing on coefficient ratios. The paper derives universal scaling relations for structure-function and hadron-nucleus cross sections that follow from the SRC framework and demonstrates that alternative volume-plus-surface interpretations can explain the same A-dependence, urging tests of coefficient-ratio scaling with future EIC and LHC light-ion data to differentiate models. Overall, while the SRC picture yields concrete, testable predictions, distinguishing SRC-origin from other volume-surface effects requires precise experimental constraints on ratio observables across a broad range of nuclei.

Abstract

We provide some critical remarks on the recently proposed two-component parametrization of nuclear parton distribution functions, which was motivated by the apparent correlation between the nuclear modifications of structure functions and nucleon-nucleon short-range correlation phenomena. This parametrization, we show, is invariant under a rescaling transformation of the involved abundance coefficients, which means that the global normalization of these coefficients cannot be meaningfully determined in a fit, and only their ratios should be studied for finding evidence of short-range-correlation type behavior at parton level. As we show, however, the current constraints for the nuclear-mass dependence of these coefficients allow also for interpretations different from short-range correlations. Nevertheless, this two-component parametrization exhibits a similar scaling relation for DIS structure functions as demonstrated in earlier works, and, as we demonstrate, yields testable predictions for structure-function and hard-process cross-section ratios. We also note on the non-trivial isospin dependence of the short-range-correlation motivated parametrization, which under proton-neutron pair dominance assumption can lead to charge-symmetry-violation resembling terms.

Scaling properties of nuclear parton distributions in short-range-correlation motivated two-component parametrization

TL;DR

This work scrutinizes a short-range correlation (SRC) motivated two-component parametrization of nuclear parton distribution functions (nPDFs). It shows a rescaling invariance prevents unique determination of the global SRC abundance normalizations, so only ratios C^A_p/C^{A_ref}_p and C^A_n/C^{A_ref}_n are physically meaningful; it offers a reformulated parametrization that avoids this issue by focusing on coefficient ratios. The paper derives universal scaling relations for structure-function and hadron-nucleus cross sections that follow from the SRC framework and demonstrates that alternative volume-plus-surface interpretations can explain the same A-dependence, urging tests of coefficient-ratio scaling with future EIC and LHC light-ion data to differentiate models. Overall, while the SRC picture yields concrete, testable predictions, distinguishing SRC-origin from other volume-surface effects requires precise experimental constraints on ratio observables across a broad range of nuclei.

Abstract

We provide some critical remarks on the recently proposed two-component parametrization of nuclear parton distribution functions, which was motivated by the apparent correlation between the nuclear modifications of structure functions and nucleon-nucleon short-range correlation phenomena. This parametrization, we show, is invariant under a rescaling transformation of the involved abundance coefficients, which means that the global normalization of these coefficients cannot be meaningfully determined in a fit, and only their ratios should be studied for finding evidence of short-range-correlation type behavior at parton level. As we show, however, the current constraints for the nuclear-mass dependence of these coefficients allow also for interpretations different from short-range correlations. Nevertheless, this two-component parametrization exhibits a similar scaling relation for DIS structure functions as demonstrated in earlier works, and, as we demonstrate, yields testable predictions for structure-function and hard-process cross-section ratios. We also note on the non-trivial isospin dependence of the short-range-correlation motivated parametrization, which under proton-neutron pair dominance assumption can lead to charge-symmetry-violation resembling terms.

Paper Structure

This paper contains 10 sections, 40 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Nuclear PDFs from SRC PDFs in two-component approach
  3. Isospin relations
  4. Rescaling invariance
  5. Relation to nuclear modification factor
  6. Reformulation of SRC-motivated parametrization
  7. Scaling relations for structure-function ratios
  8. Scaling relations for hadron-nucleus cross sections
  9. Alternative interpretation of extracted abundance coefficients
  10. Conclusion

Figures (1)

  • Figure 1: A demonstration of the volume + surface term scaling of the abundances extracted in Ref. PhysRevLett.133.152502. Left: Two-parameter fits to the $C_p^A$, $C_n^A$ coefficients. Right: One-parameter fits for the ratios $C_p^A / C_p^{A_\mathrm{ref}}$, $C_n^A / C_n^{A_\mathrm{ref}}$, and a comparison to spin-1 $pn$ contact-term ratios obtained from coordinate-space extraction of two different ab-initio QMC calculations in Ref. Cruz-Torres:2019fum. The possible correlations across different nuclei are neglected in constructing the uncertainties in the ratios.