REVIEW 4 major objections 5 minor 1 cited by
Gluonic Energy Momentum Tensor Form Factors of the Proton
T0 review · 4 major / 5 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read Near-threshold J/psi photoproduction fixes the proton's gluon mass radius at 0.755 ± 0.067 fm
desk verdict A clear proceedings summary of an already-published gluon form factor extraction; the tripole-based lattice comparison is a useful but shape-dependent addition, and the numbers should not be treated as new. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The machinery is the set of gluonic gravitational form factors defined through the nucleon matrix element of the QCD energy-momentum tensor, together with the holographic QCD formula that connects them to the $J/\psi$ photoproduction cross section. The load-bearing piece is the tripole ansatz $A_g(t)=A_g(0)(1-t/m_A^2)^{-3}$ and $C_g(t)=C_g(0)(1-t/m_C^2)^{-3}$, chosen so the fit can be compared directly with lattice QCD. Fourier transforms of $A_g$ and $D_g=4C_g$ in the Breit frame then produce the spatial mass, pressure, and shear distributions.
What would settle it
Fit the same $J/\psi$-007 differential cross sections with the fully calculated $A_g(t)$ and $D_g(t)$ shapes from the holographic model instead of the tripole ansatz, or with a different functional form such as the dipole-dipole form used in newer lattice calculations; if the resulting gluon mass radius moves outside the quoted $0.755\pm0.067$ fm uncertainty, the tripole-based extraction is not robust.
Extended reading notes
Core claim
The paper's central claim is that the $J/\psi$-007 near-threshold photoproduction cross sections constrain the gluonic gravitational form factors through the holographic QCD cross-section formula. Fitting $A_g(t)$ and $C_g(t)$ as tripoles, the paper reports $m_A=1.575\pm0.059$ GeV, $m_C=1.12\pm0.21$ GeV, and $C_g(0)=-0.45\pm0.132$, with $A_g(0)=0.414\pm0.008$ fixed by a global QCD analysis. These parameters give a gluon mass radius of $0.755\pm0.067$ fm, consistent with lattice QCD. The same form factors, with $B_g\simeq0$ and $\bar C_g$ ignored, produce Breit-frame densities for gluon energy, pressure, and shear. The paper presents this as evidence that gluonic gravitational form factors can be measured at the threshold and used to map the proton's gluon structure.
Load-bearing premise
The load-bearing premise is that the true $t$-dependence of $A_g(t)$ and $C_g(t)$ is the tripole form of Eq. (3), which the paper adopts for consistency with lattice QCD rather than deriving from the holographic model.
Editorial extensions
If this is right
- A single near-threshold measurement can determine both the gluon mass radius and the pressure profile of the proton's gluon field.
- The extracted $C_g(0)\approx -0.45$ supplies the gluon contribution to the $D$-term, the quantity that governs the internal forces felt by gluons inside the proton.
- Consistency with lattice QCD supports holographic QCD as an extraction tool for non-perturbative threshold kinematics.
- Higher-statistics measurements with a large-acceptance detector and $\Upsilon$ photoproduction at a future electron-ion collider would test whether these form factors are universal across quarkonium species and kinematics.
- Comparing these gluon densities with quark densities from deeply virtual Compton scattering would complete the two-sector picture of mass and pressure in the proton.
Reading between the lines
- Refitting the same cross sections with the holographic model's own calculated shapes for $A_g$ and $D_g$, rather than the tripole form, would show how much of the quoted $0.755$ fm radius is data-driven and how much is form-driven.
- Because the lattice comparison also uses a tripole $D(t)$ and sits at $m_\pi=400$ MeV, part of the agreement may reflect a shared fit shape; a physical-mass lattice result would be a sharper test.
- The paper argues $\bar C_g=-\bar C_q$ is positive (because $\bar C_q$ is negative), so including the ignored $\bar C_g$ term would raise the gluon energy density; the plotted density profile is then a lower bound in that sense.
- Applying the same analysis to electroproduction data at higher $Q^2$ would separate the $t$-dependence of the cross section from possible non-form-factor backgrounds, testing whether threshold photoproduction is dominated by the gluon GFFs.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This proceedings contribution reports an extraction of the gluonic gravitational form factors A_g(t) and C_g(t) of the proton from two-dimensional fits to the Hall C J/psi-007 near-threshold photoproduction cross sections. The analysis uses the Mamo-Zahed holographic QCD formula (Eq. 2) with tripole parametrizations for A_g and C_g (Eq. 3). The resulting parameters (Table 1) give a gluon mass radius sqrt(<r^2_m>)_g = 0.755 +/- 0.067 fm, consistent with the lattice result of Pefkou et al. [19]. The paper also presents Breit-frame gluon energy density, pressure, and shear force profiles (Figs. 2-3) and discusses future SoLID and EIC measurements. The fit results themselves are not tabulated or plotted in the manuscript but are attributed to private communication [29].
Significance. If the extraction is reliable, the result provides an experimentally determined gluon mass radius and mechanical densities in the proton, complementing the published Nature analysis [9] and the lattice calculations [19,26]. The paper's strength is its use of a genuinely nonperturbative holographic model and a direct comparison with lattice QCD. However, the central numerical claims are not self-contained: the fit outputs are cited to a private communication, and the tripole form assumed in Eq. (3) controls the extracted radius and profiles. Disagreement with the lattice alone is not the issue; the concern is that the agreement is reached partly by construction because both the fit and the lattice comparison adopt the same tripole ansatz. With the systematics from functional-form variation and neglected B_g and Cbar_g unquantified, the significance of the 0.755 fm radius at the quoted precision is not yet established.
major comments (4)
- [Section 3, Eq. (3), and Section 4] The tripole ansatz is the load-bearing assumption of the extraction. The text states that A_g(t) and D_g(t) shapes are fully calculated in the M-Z model [16], yet Eq. (3) replaces these shapes with a tripole 'for a consistent comparison with lattice QCD.' Since the lattice comparison [19] also uses a tripole for D_g (as stated in the Fig. 3 caption), the agreement in Table 1 is partly by construction. All quantities in Section 4 — Eq. (4) mass radius, Eqs. (5)-(7) energy density, Eq. (8) pressure and shear — are direct functions of the tripole parameters m_A and m_C. The paper provides no sensitivity test with dipole, z-expansion, or the M-Z model's own predicted shapes; without such a test the quoted 0.755 +/- 0.067 fm is not protected against bias from the chosen parametrization.
- [Section 3, Table 1, and Ref. [29]] The fit results are not present in the manuscript. Table 1 and Figures 1-3 are based on 'the J/psi-007 experiment [29] through a two-dimensional fit,' but [29] is a private communication and a talk, not a published, citable dataset. The reader cannot verify the chi-square, the t-range used, the number of data points, the treatment of correlated systematic uncertainties, or even the exact cross-section values entering the fit. A proceedings paper making a quantitative claim should either show the fit or cite a peer-reviewed article containing it; as it stands, the numerical claims are not independently checkable.
- [Section 3, after Eq. (2), and Section 4, Eq. (5)] The neglect of B_g(t) and Cbar_g(t) is acknowledged but not quantified. In Eq. (4), C_g(0) enters the mass radius with a coefficient -6/M_N^2; with C_g(0) = -0.45 +/- 0.132, the omission of Cbar_g is not obviously small, and the text itself notes (Section 4) that Cbar_g would make the gluon energy contribution larger. No estimate of the bias from B_g = 0 or Cbar_g = 0 is given, and the quoted uncertainties in Table 1 therefore exclude a known source of systematic error. This matters for the central claim of consistency with lattice at the 0.07 fm level.
- [Section 4, Figs. 2-3] The comparison with lattice is not performed on equal footing. Figure 2 states that the lattice result uses a dipole-dipole combination of form factors, while Figure 3's caption states the lattice D_g(t) is a tripole, and Section 3 says a tripole was used for all GFFs. This inconsistency in the functional forms used for different comparisons makes the visual agreement in Figs. 2-3 difficult to interpret. A single, self-consistent parametrization, or a presentation of the data points rather than curves only, would be needed to support the claim of agreement.
minor comments (5)
- [Eq. (1)] The decomposition of the EMT matrix element is written with inconsistent notation: the B-term appears as 'B_{q,g} i P^{{mu} sigma^{nu} rho} Delta_rho / (2 M_N)', which is not the standard form. Please correct the tensor indices and use a consistent convention.
- [Eq. (5)] There is a typo: the sentence says 'D_g^{FT}(r) and D_g^{FT}(r) are Fourier transform of A(t) and D(t)'. The first should be A_g^{FT}(r).
- [Figure 3 caption] The caption contains a duplicated phrase: 'the functional form of the D(t) form factor is a tripole is a tripole.'
- [Abstract and Section 2] The abstract states the analysis uses data from 'electronic decay channels,' but Section 2 says both e+e- and mu+mu- pair decays were detected; please harmonize the wording.
- [References] Reference [21] appears in the reference list but is not cited in the body of the text.
Circularity Check
No circular derivation: the gluonic form factors are fitted to external J/psi-007 cross-section data and the mass radius is a standard transform of those fitted form factors; the tripole ansatz is an explicit assumption, not a self-referential input.
full rationale
The derivation chain begins with the M-Z holographic cross-section formula (Eq. 2), which depends on A_g(t) and D_g(t), and the measured J/psi-007 differential cross sections. The paper fits the free parameters m_A, C_g(0), and m_C in the tripole forms of Eq. (3) to these external data, with A_g(0) fixed by the CT18 global PDF analysis. The mass radius in Eq. (4) and the density profiles in Eqs. (5)-(8) are obtained by differentiating and Fourier transforming the fitted form factors; these are derived quantities from the same fit rather than independent predictions, but that is ordinary inverse-problem inference, not circularity. The comparison with lattice QCD uses the independent calculation of Ref. [19]. The paper explicitly states that the tripole form was chosen 'for a consistent comparison with lattice QCD calculations' and notes in Fig. 1 that 'in all cases the form factors used are of tripole functional form'; this is a transparent parametrization assumption that could bias the extracted values if the true t-dependence is non-tripole, but it is not a reduction of the result to its inputs. Self-citations appear (Refs. [9] and [29] report the same experiment's data and fit results, and Refs. [11,16,22] are the M-Z model), but the central input data are external and the lattice benchmark is independent; no equation in the paper is equal by construction to the claimed output.
Assumptions & free parameters
free parameters (5)
- A_g(0) (gluon momentum fraction) =
0.414 (fixed from CT18 global fit, +/- 0.008)
- m_A =
1.575 +/- 0.059 GeV
- m_C =
1.12 +/- 0.21 GeV
- C_g(0) =
-0.45 +/- 0.132
- N^2 e^2 normalization in Eq. 2 =
(7.768)^2 nb/GeV^6
assumptions (6)
- domain assumption The Mamo-Zahed holographic QCD cross-section formula (Eq. 2) is the correct description of near-threshold J/psi photoproduction.
- domain assumption Tripole functional forms (Eq. 3) accurately represent the t-dependence of A_g and C_g.
- domain assumption B_g(t) can be set to zero and Cbar_g(t) ignored.
- domain assumption CT18 gluon momentum fraction provides the correct A_g(0).
- domain assumption Lattice QCD at m_pi=400 MeV is a valid benchmark for the proton.
- standard math Standard Breit-frame Fourier transform relations (Lorce et al. [25]) connect the form factors to spatial densities.
Cite this review
Pith. "Pith review of Gluonic Energy Momentum Tensor Form Factors of the Proton." pith.science (2026). https://pith.science/paper/PAVVFHA2
@misc{pith2026250505671,
author = {Pith},
title = {Pith review of: Gluonic Energy Momentum Tensor Form Factors of the Proton},
year = {2026},
howpublished = {\url{https://pith.science/paper/PAVVFHA2}},
note = {Machine review of arXiv:2505.05671}
}
abstract
Gravitational form factors (GFFs), defined through the matrix elements of the energy-momentum tensor, provide critical insights into the internal structure of nucleons and nuclei. In particular, their Fourier transforms -- evaluated in the Breit frame -- reveal spatial distributions of mass, pressure, and shear force densities associated with both quark and gluon constituents. This work presents recent measurements of near-threshold $J/\psi$ photoproduction on the proton, performed in Hall C at Jefferson Lab, utilizing data from the electronic decay channels of the $J/\psi$. These results enable the extraction of gluonic gravitational form factors (gGFFs), offering a novel probe of the gluon dynamics within the nucleon. The analysis employs a holographic QCD framework to interpret the threshold behavior of the cross sections and to facilitate the extraction of the gGFFs. The implications of these measurements are discussed in the context of upcoming experimental programs, including the near-threshold electro- and photoproduction studies with SoLID at Jefferson Lab and the $\Upsilon$ production program at the Electron-Ion Collider using the ePIC detector. These future efforts are expected to significantly improve the precision of gGFF determinations and provide essential tests of their universality across different kinematic regimes.
Figures
Forward citations
Cited by 1 Pith paper
-
On the Impossibility of Obtaining Time-Independent, Three-Dimensional, Spherically-Symmetric Densities of Confined Systems of Relativistically Moving Constituents
Time-independent three-dimensional spherical densities cannot be defined for relativistic confined systems; only transverse two-dimensional light-front densities are consistent with quantum mechanics and Poincare invariance.
Reference graph
Works this paper leans on
- [9]
-
[19]
D. A. Pefkou, D. C. Hackett and P. E. Shanahan,Gluon gravitational structure of hadrons of different spin,Phys. Rev. D105, no.5, 054509 (2022), doi:10.1103/PhysRevD.105.054509, [hep-lat/2107.10368]
arXiv 2022
-
[29]
Probing the gluonic gravitational form factors of the proton using near-threshold𝐽/𝜓photoproduction
S. Prasad, Private communication and " Probing the gluonic gravitational form factors of the proton using near-threshold𝐽/𝜓photoproduction", Hall C Winter Collaboration meet- ing,January18-19,2024,NewwportNews,VA,https://indico.jlab.org/event/758/ contributions/13800/ 9
work page 2024
-
[16]
K. A. Mamo and I. Zahed,J/𝜓near-threshold in holographic QCD: A and D gravitational form factors,Phys. Rev. D106, no.8, 086004 (2022), doi:10.1103/PhysRevD.106.086004 [hep-ph/2204.08857 hep-ph]
arXiv 2022
-
[1]
V. D. Burkert, L. Elouadrhiri, F. X. Girod, C. Lorcé, P. Schweitzer and P. E. Shanahan, Colloquium: Gravitational form factors of the proton,Rev. Mod. Phys.95(2023) no.4, 041002 doi:10.1103/RevModPhys.95.041002, [hep-ph/2303.08347]
arXiv 2023
-
[2]
X.D.Ji,Gauge-InvariantDecompositionofNucleonSpin,Phys.Rev.Lett.78,610-613(1997) doi:10.1103/PhysRevLett.78.610 [hep-ph/9603249]
arXiv 1997
-
[3]
V. D. Burkert, L. Elouadrhiri and F. X. Girod,The pressure distribution inside the proton,’ Nature557(2018) no.7705, 396-399, doi:10.1038/s41586-018-0060-z
-
[4]
Phys.127, 103985 (2022) doi:10.1016/j.ppnp.2022.103985, [nucl-ex/2112.00060]
J.Arrington,etal.,PhysicswithCEBAFat12GeVandfutureopportunities,Prog.Part.Nucl. Phys.127, 103985 (2022) doi:10.1016/j.ppnp.2022.103985, [nucl-ex/2112.00060]
Show all 29 references
-
[5]
Abdul Khalek,et al.,Science Requirements and Detector Concepts for the Electron-Ion Collider: EIC Yellow Report,Nucl
R. Abdul Khalek,et al.,Science Requirements and Detector Concepts for the Electron-Ion Collider: EIC Yellow Report,Nucl. Phys. A1026(2022), 122447 doi:10.1016/j.nuclphysa.2022.122447, [physics.ins-det/2103.05419]
2022
-
[6]
Lorcé, A
C. Lorcé, A. Metz, B. Pasquini and S. Rodini,Energy-momentum tensor in QCD: nucleon mass decomposition and mechanical equilibrium,JHEP11, 121 (2021), doi:10.1007/JHEP11(2021)121, [hep-ph/2109.11785]
2021 arXiv
-
[7]
X.D.Ji,AQCDanalysisofthemassstructureofthenucleon,Phys.Rev.Lett.74,1071-1074 (1995) doi:10.1103/PhysRevLett.74.1071 [hep-ph/9410274]
1995 arXiv
-
[8]
Z.-E.Meziani,S.Joosten,M.Paolone,E.Chudakov,M.Jones,K.Adhikari,K.Aniol,W.Arm- strong,J.ArringtonandA.Asaturyan,etal.ASearchfortheLHCbCharmed’Pentaquark’us- ingPhoto-Productionof𝐽/𝜓atThresholdinHallCatJeffersonLab,[hep-ex/1609.00676]
-
[10]
D. E. Kharzeev,Mass radius of the proton,Phys. Rev. D104(2021) no.5, 054015, doi:10.1103/PhysRevD.104.054015 [hep-ph/2102.00110]. 7 Gluonic Energy Momentum Tensor Form Factors of the ProtonZein-Eddine Meziani
2021 arXiv
-
[11]
K.A.MamoandI.Zahed,Diffractivephotoproductionof𝐽/𝜓andΥusingholographicQCD: gravitational form factors and GPD of gluons in the proton,Phys. Rev. D101, no.8, 086003 (2020), doi:10.1103/PhysRevD.101.086003, [hep-ph/1910.04707]
2020 arXiv
-
[12]
Y.Guo,X.JiandY.Liu,QCDAnalysisofNear-ThresholdPhoton-ProtonProductionofHeavy Quarkonium,Phys. Rev. D103, no.9, 096010 (2021), doi:10.1103/PhysRevD.103.096010
2021 doi
-
[13]
Hatta and D
Y. Hatta and D. L. Yang,Holographic𝐽/𝜓production near-threshold and the proton mass problem,Phys. Rev. D98(2018) no.7, 074003, doi:10.1103/PhysRevD.98.074003 [hep-ph/1808.02163]
2018 arXiv
-
[14]
Hatta, A
Y. Hatta, A. Rajan and D. L. Yang,Near-threshold𝐽/𝜓andΥphotoproduction at JLab and RHIC,Phys. Rev. D100(2019) no.1, 014032, doi:10.1103/PhysRevD.100.014032 [hep-ph/1906.00894]
2019 arXiv
-
[15]
P. Sun, X. B. Tong and F. Yuan,Perturbative QCD analysis of near-threshold heavy quarko- nium photoproduction at large momentum transfer,Phys. Lett. B822(2021), 136655, doi:10.1016/j.physletb.2021.136655, [hep-ph/2103.12047]
2021
-
[17]
Adhikariet al.[GlueX],Measurement of the J/𝜓photoproduction cross section over the full near-threshold kinematic region,Phys
S. Adhikariet al.[GlueX],Measurement of the J/𝜓photoproduction cross section over the full near-threshold kinematic region,Phys. Rev. C108, no.2, 025201 (2023), doi:10.1103/PhysRevC.108.025201, [nucl-ex/2304.03845]
2023 arXiv
-
[18]
Y. Guo, F. Yuan and W. Zhao,Bayesian Inferring Nucleon’s Gravitation Form Factors via Near-threshold𝐽/𝜓Photoproduction,[arXiv:2501.10532 [hep-ph]]
-
[20]
T. J. Hou, J. Gao, T. J. Hobbs, K. Xie, S. Dulat, M. Guzzi, J. Huston, P. Nadolsky, J. Pumplin and C. Schmidt,et al. New CTEQ global analysis of quantum chromody- namics with high-precision data from the LHC,Phys. Rev. D103, no.1, 014013 (2021), doi:10.1103/PhysRevD.103.014013...
2021 arXiv
-
[21]
Y. Guo, X. Ji, Y. Liu and J. Yang,“Updated analysis of near-threshold heavy quarkonium production for probe of proton’s gluonic gravitational form factors,Phys. Rev. D108, no.3, 034003 (2023), doi:10.1103/PhysRevD.108.034003 [hep-ph/2305.06992]
2023 arXiv
-
[22]
K. A. Mamo and I. Zahed,Nucleon mass radii and distribution: Holographic QCD, Lattice QCD and GlueX data,Phys. Rev. D103, no.9, 094010 (2021), doi:10.1103/PhysRevD.103.094010, [hep-ph/2103.03186]. 8 Gluonic Energy Momentum Tensor Form Factors of the ProtonZein-Eddine Meziani
2021 arXiv
-
[23]
Arringtonet al.[Jefferson Lab SoLID],The solenoidal large intensity device (SoLID) for JLab 12 GeV,J
J. Arringtonet al.[Jefferson Lab SoLID],The solenoidal large intensity device (SoLID) for JLab 12 GeV,J. Phys. G50(2023) no.11, 110501, doi:10.1088/1361-6471/acda21, [nucl-ex/2209.13357]
2023 arXiv
-
[24]
Gryniuk, S
O. Gryniuk, S. Joosten, Z.-E. Meziani and M. Vanderhaeghen,Υphotoproduction on the proton at the Electron-Ion Collider,Phys. Rev. D102, no.1, 014016 (2020), doi:10.1103/PhysRevD.102.014016, [hep-ph/2005.09293]
2020 arXiv
-
[25]
Lorcé, H
C. Lorcé, H. Moutarde and A. P. Trawiński,Revisiting the mechanical properties of the nucleon,Eur. Phys. J. C79(2019) no.1, 89 doi:10.1140/epjc/s10052-019-6572-3, [hep-ph/1810.09837 hep-ph]
2019 arXiv
-
[26]
D. C. Hackett, D. A. Pefkou and P. E. Shanahan,Gravitational Form Factors of the Proton from Lattice QCD,Phys. Rev. Lett.132(2024) no.25, 251904, doi:10.1103/PhysRevLett.132.251904, [hep-lat/2310.08484]
2024 arXiv
-
[27]
Hatta, A
Y. Hatta, A. Rajan and K. Tanaka,Quark and gluon contributions to the QCD trace anomaly, JHEP12, 008 (2018), doi:10.1007/JHEP12(2018)008, [hep-ph/1810.05116]
2018 arXiv
-
[28]
K.Tanaka,Twist-fourgravitationalformfactoratNNLOQCDfromtraceanomalyconstraints, JHEP03, 013 (2023), doi:10.1007/JHEP03(2023)013 [hep-ph/2212.09417]
2023 arXiv
Reviewed August 15, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.