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arxiv: 2606.17133 · v1 · pith:PKX7ARRMnew · submitted 2026-06-15 · ✦ hep-ph · nucl-ex· nucl-th

Short-Range Correlations Between Partons in a Proton

Jen-Chieh Peng , Krishna Rajagopal , John Terry This is my paper

Pith reviewed 2026-06-27 03:11 UTC · model grok-4.3

classification ✦ hep-ph nucl-exnucl-th
keywords short-range correlationsparton correlationsproton structureElectron-Ion Colliderdiquark attractionisospin dependencequark-gluon plasmajet-pion observables
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The pith

EIC measurements of a jet and a pion with the scattered electron can detect short-range correlations between quark pairs inside protons.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper argues that the energy density and pressure inside a proton are comparable to those in quark-gluon plasma, so correlations between nearby partons deserve direct study at the future Electron-Ion Collider. It proposes that observables combining a jet, a pion, and the scattered electron can reveal and quantify short-range correlations among quark pairs. The proposal rests on an analogy to nucleon short-range correlations in nuclei, where neutron-proton pairs dominate; here the QCD attraction in the ud diquark channel is expected to make ud quark pairs more strongly correlated than uu or dd pairs. If observed, these partonic correlations would add a new layer to proton structure beyond single-parton distributions and supply insight into why quark-gluon plasma behaves as a strongly coupled liquid.

Core claim

The central claim is that EIC observables involving measurements of a jet and a pion together with the scattered electron can seek and quantify the possible existence of short-range correlations between quark pairs within a nucleon, with the QCD attraction in the ud diquark channel making ud SRCs stronger than uu or dd SRCs and thereby allowing a first observation of partonic SRCs.

What carries the argument

The proposed EIC jet-plus-pion measurement that exploits the isospin dependence arising from QCD attraction in the ud diquark channel, in direct analogy to the np dominance seen in nuclear SRCs.

If this is right

  • The measurements would characterize the strongly coupled interior of the proton beyond the one-parton-at-a-time picture from generalized parton distributions.
  • They would provide a key ingredient for a microscopic understanding of the liquid nature of quark-gluon plasma.
  • They would enable the first observation of partonic short-range correlations.
  • The isospin asymmetry in the signals would directly test the role of diquark attraction at the parton level.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the signals are observed, similar jet-pion measurements could be pursued in other high-energy experiments to map parton correlations across different hadrons.
  • The approach would connect nuclear SRC studies to the partonic structure of free nucleons, suggesting a unified description across length scales.
  • Confirmation would motivate theoretical calculations of the expected ud enhancement using models of diquark correlations inside the proton.

Load-bearing premise

The isospin dependence and dominance pattern observed for nucleon SRCs in nuclei has a direct analog for partonic SRCs inside protons driven by the QCD attraction in the ud diquark channel.

What would settle it

Data from the proposed EIC jet-plus-pion observables showing no enhancement of ud correlations relative to uu or dd correlations would falsify the predicted partonic SRCs.

Figures

Figures reproduced from arXiv: 2606.17133 by Jen-Chieh Peng, John Terry, Krishna Rajagopal.

Figure 1
Figure 1. Figure 1: FIG. 1: Schematic illustration of the observable used to [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Laboratory pseudorapidity distribution of the [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Breit frame azimuthal angle correlation between [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
read the original abstract

A principal lesson from recreating droplets of quark-gluon plasma (QGP) in heavy ion collisions is that it is a strongly coupled liquid, not a plasma of partons. The energy density and pressure of quarks and gluons confined within a proton are comparable to those of QGP at or just above the QCD transition temperature. Given this similarity between protons and QGP, we propose that the investigation of correlations between nearby partons within a proton must be a central goal for the future Electron-Ion Collider (EIC). Here, we ask how EIC measurements can discern such short-range correlations (SRCs) of quark pairs. Doing so would characterize the strongly coupled interior of a proton, augmenting the one-parton-at-a-time understanding of protons via (generalized) parton distribution functions, and could at the same time yield a key ingredient for the microscopic understanding of the liquid nature of QGP. Motivated by the experiments that have been used to demonstrate the existence of SRCs between nucleon pairs within a nucleus, we propose using EIC observables involving measurements of a jet and a pion, together with the scattered electron, to seek and quantify the possible existence of SRCs between quark pairs within a nucleon. The pronounced isospin dependence observed in the dominance of $np$ SRCs over $pp$ or $nn$ SRCs has played a central role in establishing the importance of SRCs among nucleons in nuclei. Analogously, the QCD attraction in the $ud$ diquark channel can make the $ud$ SRC stronger than the $uu$ and $dd$ SRCs, allowing a first observation of partonic SRCs.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript proposes that EIC triple-coincidence measurements of a jet, a pion, and the scattered electron can seek and quantify short-range correlations (SRCs) between quark pairs inside a proton. It motivates the idea from the strongly coupled liquid-like nature of both the proton interior and QGP, and argues that the isospin pattern seen in nuclear SRCs (np dominance) should have a partonic analog driven by QCD attraction in the ud diquark channel, making ud SRCs stronger than uu or dd and enabling a first observation of partonic SRCs.

Significance. If the proposed observables can isolate partonic SRCs, the work would extend the one-parton-at-a-time description provided by GPDs to correlated multi-parton structure inside the nucleon and supply a potential microscopic ingredient for understanding the liquid nature of QGP. The analogy-based proposal is novel in its direct transfer of nuclear-physics concepts to the partonic level at an upcoming collider.

major comments (2)
  1. [Abstract] Abstract: the claim that the jet+pion+electron observables 'can seek and quantify' SRCs between quark pairs rests on an untested assumption that the nuclear np-dominance pattern has a direct counterpart at the parton level; no calculation, toy model, or kinematic estimate is supplied to show that a ud excess would be measurable above standard PDFs, fragmentation, or other correlations.
  2. [Abstract] Abstract: the assertion that 'the QCD attraction in the ud diquark channel can make the ud SRC stronger' and thereby allow 'a first observation of partonic SRCs' is presented solely by analogy without any supporting argument or estimate demonstrating why the nuclear isospin pattern should translate to partons inside a single proton.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments. The points raised correctly identify that the abstract's claims rely on an untested analogy without quantitative support. We address each comment below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that the jet+pion+electron observables 'can seek and quantify' SRCs between quark pairs rests on an untested assumption that the nuclear np-dominance pattern has a direct counterpart at the parton level; no calculation, toy model, or kinematic estimate is supplied to show that a ud excess would be measurable above standard PDFs, fragmentation, or other correlations.

    Authors: We agree that the abstract phrasing implies a stronger claim than is supported by explicit calculations in the manuscript. The work is a conceptual proposal to motivate EIC measurements based on the nuclear SRC analogy. We will revise the abstract to state that the observables 'could be used to search for and potentially quantify' such correlations, and add a brief discussion of how one might estimate the expected ud excess using simple scaling from nuclear data and known diquark properties. revision: yes

  2. Referee: [Abstract] Abstract: the assertion that 'the QCD attraction in the ud diquark channel can make the ud SRC stronger' and thereby allow 'a first observation of partonic SRCs' is presented solely by analogy without any supporting argument or estimate demonstrating why the nuclear isospin pattern should translate to partons inside a single proton.

    Authors: The manuscript presents the ud dominance as a hypothesis motivated by the parallel between the attractive np channel in nuclei and the attractive ud diquark channel in QCD, together with the comparable energy densities in the proton and near-Tc QGP. We acknowledge that no quantitative estimate or detailed mapping is provided. We will revise the abstract and introduction to clarify this as a motivated conjecture to be tested experimentally, and add references to existing theoretical work on diquark correlations inside nucleons. revision: yes

Circularity Check

0 steps flagged

No circularity; proposal paper with no derivations or fitted quantities

full rationale

The manuscript is a conceptual proposal for EIC measurements of partonic SRCs, motivated by nuclear SRC analogies and QCD diquark attraction. No equations, normalizations, parameter fits, or self-citation chains appear in the provided text. The central claim is an unverified conjecture resting on analogy, not a derivation that reduces to its inputs by construction. This matches the default expectation of no circularity for non-derivational papers.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The proposal rests on the domain assumption that diquark-channel attraction produces an isospin dependence in partonic SRCs analogous to that seen in nuclei; no free parameters or new entities are introduced in the abstract.

axioms (1)
  • domain assumption The QCD attraction in the ud diquark channel produces stronger ud SRCs than uu or dd SRCs, mirroring the np dominance in nuclear SRCs
    Invoked in the final sentence of the abstract to motivate the expected experimental signature.

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discussion (0)

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