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arxiv: 2210.12295 · v2 · submitted 2022-10-21 · ✦ hep-ph · hep-ex· nucl-th

Accessing gluon polarization with high-P_T hadrons in SIDIS

R. M. Whitehill , Yiyu Zhou , N. Sato , W. Melnitchouk This is my paper

Pith reviewed 2026-05-24 10:42 UTC · model grok-4.3

classification ✦ hep-ph hep-exnucl-th
keywords gluon helicitySIDIShigh transverse momentumdouble spin asymmetryproton spin structureQCD global analysisJefferson LabElectron-Ion Collider
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The pith

Polarized SIDIS with high transverse momentum hadrons can discriminate between positive and negative solutions for the gluon helicity distribution Δg.

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

The paper investigates polarized semi-inclusive deep-inelastic scattering producing hadrons at large transverse momentum as a probe of the gluon helicity distribution Δg(x) inside the proton. Recent global QCD analyses have identified both the conventional positive Δg and new negative solutions, and the work maps kinematics where the double longitudinal spin asymmetry isolates the gluon contribution. Specific ranges accessible at Jefferson Lab and the Electron-Ion Collider are shown to be especially sensitive to the x-dependence of Δg. This setup offers a practical route to test which sign behavior is realized by nature.

Core claim

The double longitudinal spin asymmetry for high-P_T hadrons in polarized SIDIS receives a dominant contribution from the polarized gluon channel in selected kinematics, enabling discrimination between the positive and negative Δg behaviors found in global fits.

What carries the argument

Double longitudinal spin asymmetry in high transverse momentum hadron production, which isolates the polarized gluon contribution when higher-order and quark terms are controlled.

If this is right

  • The asymmetry provides direct sensitivity to the x-dependence of Δg at moderate to small momentum fractions.
  • Kinematics can be chosen to suppress quark-initiated channels and highlight gluon polarization effects.
  • Data from such measurements would enter global QCD analyses and help resolve the sign ambiguity in Δg.
  • The approach applies at the beam energies planned for Jefferson Lab and the Electron-Ion Collider.

Where Pith is reading between the lines

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

  • Combining these asymmetries with inclusive jet or dijet data could tighten constraints on the full shape of Δg(x).
  • If negative Δg solutions are favored, existing models of how gluon spin contributes to the proton's total spin would require revision.
  • The method suggests a concrete observable priority list for early running at the EIC.

Load-bearing premise

The double longitudinal spin asymmetry remains dominated by the polarized gluon channel once higher-order corrections and quark contributions are accounted for in the chosen kinematics.

What would settle it

A precise measurement of the double longitudinal spin asymmetry in the identified high-P_T kinematics at JLab or EIC energies that fails to match the gluon-channel predictions from either the positive or negative Δg sets.

Figures

Figures reproduced from arXiv: 2210.12295 by N. Sato, R. M. Whitehill, W. Melnitchouk, Yiyu Zhou.

Figure 1
Figure 1. Figure 1: FIG. 1. Polarized gluon distribution [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Inclusive double spin asymmetry for [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Sketch of the diagram representing SIDIS of a lepton (momentum [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Diagrams representing squared amplitudes for virtual Compton scattering from a parton [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Available kinematics at Jefferson Lab with a 12 GeV (top row) and 22 GeV (middle row) [PITH_FULL_IMAGE:figures/full_fig_p016_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Double longitudinal spin asymmetry [PITH_FULL_IMAGE:figures/full_fig_p017_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. Unpolarized (solid bands) and polarized (hatched bands) differential cross sections calcu [PITH_FULL_IMAGE:figures/full_fig_p019_7.png] view at source ↗
read the original abstract

A recent global QCD analysis of jet production and other polarized scattering data has found the presence of negative solutions for the gluon helicity distribution in the proton, $\Delta g$, along with the traditional $\Delta g > 0$ solutions. We consider polarized semi-inclusive deep-inelastic scattering for hadrons produced with large transverse momentum as a means of constraining the dependence of $\Delta g$ on the parton momentum fraction, $x$. Focusing on the double longitudinal spin asymmetry, we identify the kinematics relevant for future experiments at Jefferson Lab and the Electron-Ion Collider which are particularly sensitive to the polarized gluon channel and could discriminate between the different $\Delta g$ behaviors.

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

1 major / 1 minor

Summary. The manuscript proposes using the double longitudinal spin asymmetry A_LL in polarized semi-inclusive deep-inelastic scattering (SIDIS) with high-P_T hadrons to constrain the x-dependence of the gluon helicity distribution Δg and discriminate between the positive and negative solutions identified in recent global QCD analyses. It focuses on identifying kinematics at Jefferson Lab and the Electron-Ion Collider where the polarized gluon channel is particularly sensitive.

Significance. If the central assumption of controllable gluon dominance holds, the work would supply a useful new observable for resolving sign ambiguities in Δg at moderate x, complementing existing jet and inclusive data. The approach rests on standard pQCD factorization without introducing new parameters or entities.

major comments (1)
  1. [Kinematic selection and asymmetry discussion (near the partonic subprocess analysis)] The central claim that selected high-P_T kinematics discriminate Δg > 0 vs. negative solutions requires A_LL to be gluon-dominated with controllable quark and higher-order pieces. The manuscript identifies sensitive regions via partonic kinematics but provides no explicit fractional breakdown (gluon vs. quark channels, LO vs. NLO) or variation with x in the JLab/EIC bins, leaving the discriminatory power unquantified.
minor comments (1)
  1. Notation for the partonic subprocesses and scale choices could be made more uniform across figures and text.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive report and positive assessment of the potential utility of the proposed observable. We address the single major comment below and will incorporate the requested quantification in a revised manuscript.

read point-by-point responses

  1. Referee: [Kinematic selection and asymmetry discussion (near the partonic subprocess analysis)] The central claim that selected high-P_T kinematics discriminate Δg > 0 vs. negative solutions requires A_LL to be gluon-dominated with controllable quark and higher-order pieces. The manuscript identifies sensitive regions via partonic kinematics but provides no explicit fractional breakdown (gluon vs. quark channels, LO vs. NLO) or variation with x in the JLab/EIC bins, leaving the discriminatory power unquantified.

    Authors: We agree that an explicit fractional breakdown of the gluon versus quark channels (and LO versus NLO contributions) as a function of x would strengthen the central claim and better quantify the discriminatory power. While the manuscript selects kinematics on the basis of partonic subprocess dominance, we did not provide the requested numerical decomposition. In the revised version we will add figures (or tables) that display the relative contributions to A_LL from the dominant gluon-initiated channels versus quark channels, together with an estimate of NLO corrections, evaluated in the JLab and EIC bins under consideration. This will make the degree of gluon dominance and its x-dependence explicit. revision: yes

Circularity Check

0 steps flagged

No significant circularity; standard pQCD factorization applied to new observable

full rationale

The paper applies established perturbative QCD factorization theorems to the double longitudinal spin asymmetry in high-P_T SIDIS, identifying kinematics sensitive to Δg via partonic subprocesses. No derivation step reduces by the paper's own equations to a fitted input or self-cited uniqueness result; the mapping from A_LL to Δg relies on external global analyses and standard assumptions without internal self-definition or renaming of known results. The central claim remains independent of any load-bearing self-citation chain.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper relies on standard perturbative QCD factorization for SIDIS and on the existence of the negative Δg solutions reported in a cited global analysis; no new free parameters, ad-hoc axioms, or invented entities are introduced.

axioms (1)
  • standard math Standard collinear factorization applies to polarized SIDIS at the kinematics considered
    Invoked when mapping the double longitudinal spin asymmetry to Δg sensitivity.

pith-pipeline@v0.9.0 · 5650 in / 1214 out tokens · 22379 ms · 2026-05-24T10:42:18.323399+00:00 · methodology

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Reference graph

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