{"id":"c308a795-f960-4f8c-885e-bde093e8e521","arxiv_id":"2505.05671","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":2.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Near-threshold J/psi photoproduction data from Jefferson Lab Hall C, interpreted with a holographic QCD model and tripole form factors, give a gluon mass radius of about 0.755 fm and pressure and shear profiles consistent with lattice QCD.","lead":"A JLab Hall C measurement of near-threshold J/psi photoproduction is used, together with a holographic QCD model, to extract the gluon gravitational form factors of the proton and a gluon mass radius of about 0.755 fm. It shows how heavy-quark photoproduction can image the gluon distribution of mass and pressure inside the proton.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Tripole ansatz in Eq. (3) is load-bearing: the paper replaces the model's own computed A_g/D_g shapes with an ad hoc tripole and compares to lattice using the same tripole, so the claimed mass radius is shape-dependent.","rationale":"After reading the paper in good faith, the central claim is the extraction of gluonic GFFs and a gluon mass radius from J/psi-007 data via the M-Z holographic formula, with the tripole form for A_g and C_g. The most load-bearing assumption is that the tripole form (Eq. 3) faithfully represents the true t-dependence of the gluon form factors over the measured range. The paper acknowledges that M-Z provides 'fully calculated' shapes but then discards them in favor of the tripole solely for lattice comparison. This is not a minor point: every quantitative result in Table 1 and Section 4 (mass radius, density, pressure, shear) is computed from the tripole parameters. Moreover, because the lattice comparison [19] also uses a tripole, the consistency in Table 1 is partly a statement about parameters within the same ansatz, not a test of the ansatz itself. Other limitations (private communication for fit values, proceedings-level brevity, neglect of B_g and Cbar_g, model dependence of Eq. 2) are real but secondary; they affect reproducibility and absolute systematics, while the tripole assumption directly determines the headline number. The reader's verdict of CONDITIONAL is therefore appropriate. Our concrete test — refitting with the M-Z model's own predicted shapes — would settle whether the tripole is responsible for the claimed radius. If the radius is stable under that change, the concern is resolved; if not, the paper's headline claim as stated is not supported.","tokens_in":7980,"tokens_out":12368,"duration_ms":126087,"concrete_test":"Refit the J/ψ-007 two-dimensional cross sections using the Mamo–Zahed model's own computed A_g(t) and D_g(t) from Ref. [16] in Eq. (2), with only the overall normalization (and, if required, an overall scale of D_g) free; compare the chi-squared and the mass radius from Eq. (4) to Table 1. If the mass radius shifts by more than the quoted ±0.067 fm, the tripole ansatz is the load-bearing assumption.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 3 states that 'A_g(t) and D_g(t) shapes are fully calculated in this model' (Mamo–Zahed) and then immediately imposes the tripole form of Eq. (3) 'for a consistent comparison with lattice QCD.' This is the central weak point: the extraction uses the M-Z cross-section formula (Eq. 2) but not the model's predicted t-dependence. All derived quantities in Section 4 — the mass radius (Table 1), the energy density, pressure, and shear profiles (Figs. 2–3) — are integrals/derivatives of the tripole A_g and D_g. If the true gluon form factors deviate from tripole behavior in the fitted t-range, the fitted m_A, m_C, and C_g(0) are biased. The agreement with lattice is also partly by construction, since the lattice comparison [19] itself uses tripole fits; a shared wrong ansatz would produce spurious agreement. The paper provides no cross-check with alternative parametrizations (e.g., dipole, z-expansion) or with the model's own shapes, and the fit results are only available via private communication [29], preventing independent verification.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","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].","tokens_in":8172,"tokens_out":6119,"duration_ms":64465,"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":[{"comment":"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":"Section 3, Eq. (3), and Section 4"},{"comment":"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":"Section 3, Table 1, and Ref. [29]"},{"comment":"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":"Section 3, after Eq. (2), and Section 4, Eq. (5)"},{"comment":"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.","section":"Section 4, Figs. 2-3"}],"minor_comments":[{"comment":"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.","section":"Eq. (1)"},{"comment":"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).","section":"Eq. (5)"},{"comment":"The caption contains a duplicated phrase: 'the functional form of the D(t) form factor is a tripole is a tripole.'","section":"Figure 3 caption"},{"comment":"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.","section":"Abstract and Section 2"},{"comment":"Reference [21] appears in the reference list but is not cited in the body of the text.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a conference proceedings that relies heavily on the author's own prior work [9] and on an unpublished private communication [29]. For a journal, the editor may wish to consider whether the technical content is sufficient without the accompanying full paper; at minimum, the fit results and fit quality must be made available for independent assessment. No concerns about novelty beyond this."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a PoS proceedings summary of the J/psi-007 gluon GFF extraction already published in Duran et al., Nature 615, 813 (2023) (ref [9] here). The numbers—gluon mass radius 0.755±0.067 fm, the A_g and D_g curves—are not new. What is new in this writeup is a lattice comparison using tripole form factors for both experiment and lattice, plus a clean statement of the model assumptions.\n\nThe paper does several things well. It lays out the EMT decomposition, explains why J/psi photoproduction can probe gluon GFFs, and is transparent about what is dropped: B_g(t) is set to zero and Cbar_g(t) ignored. The comparison to lattice Ref. [19] is honest, and the author notes the lattice runs at m_pi=400 MeV. For a proceedings, the level of detail is about right.\n\nThe soft spot is the tripole ansatz, and it is load-bearing. In Sec. 3 the author states the Mamo-Zahed model gives fully calculated A_g(t) and D_g(t) shapes, then immediately replaces them with Eq. (3) tripoles 'for a consistent comparison with lattice.' Since the lattice calculation in [19] itself uses tripole fits, part of the agreement is by construction. The mass radius in Eq. (4) and all density profiles in Sec. 4 are derived from that tripole shape, so they are affected by the choice. There are no cross-checks with other parametrizations (dipole, z-expansion) or with the model's own shapes. This is a real limitation, but it's an explicitly disclosed modeling choice, not a logical contradiction or hidden circularity.\n\nThe other issue is reproducibility: Table 1 is attributed to a private communication [29], and the fit procedure relies on cross-section data published elsewhere. A reader cannot independently verify the numbers from this paper alone. For a proceedings summary that's conventional; for a standalone research paper it would be a problem.\n\nBottom line: the paper is a fair status report from an ongoing program, and the tripole-dependent results are plausible and consistent with lattice. I would not treat it as a new result or cite it in place of the Nature paper. If it's meant as a PoS contribution, it's fine as is. If it's submitted as a research article, it needs the fit details, public data, and alternative parametrization checks before referees can evaluate it.\n\nMy recommendation: don't send this to a full referee round as a new research paper; the substantive physics already passed review at Nature. If your venue requires proceedings review, a light check for accurate reporting is enough.","headline":"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.","tokens_in":8758,"tokens_out":5263,"would_cite":false,"duration_ms":57119,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":false},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Near-threshold J/psi photoproduction fixes the proton's gluon mass radius at 0.755 ± 0.067 fm","keywords":["gluonic gravitational form factors","energy-momentum tensor","near-threshold J/psi photoproduction","gluon mass radius","holographic QCD","pressure and shear distributions","J/psi-007 experiment","lattice QCD"],"falsifier":"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.","tokens_in":7692,"feed_emoji":"⚛️","tokens_out":16389,"duration_ms":149915,"temperature":0.7,"pith_summary":"This paper reports that near-threshold photoproduction of the $J/\\psi$ on the proton, measured in a Hall C experiment, can be used to extract the gluonic gravitational form factors $A_g(t)$ and $C_g(t)$ of the proton. Using a non-perturbative holographic QCD model and a two-dimensional fit of the differential cross section in photon energy and momentum transfer $t$, the paper obtains a gluon mass radius of $\\sqrt{\\langle r^2_m\\rangle_g}=0.755\\pm0.067$ fm. This value agrees with the lattice QCD result of $0.7464\\pm0.055$ fm. The extracted form factors are then Fourier-transformed in the Breit frame to give the gluon energy, pressure, and shear force densities. The reader should care because gluons dominate the proton's mass, and these densities are currently the main experimental window into how that mass is spatially distributed.","feed_headline":"Near-threshold data fix proton's gluon radius at 0.755 fm","feed_subtitle":"J/psi photoproduction near threshold, fitted with holographic QCD, gives a gluon radius consistent with lattice QCD.","key_machinery":"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.","core_discovery":"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.","pith_inferences":["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."],"forward_implications":["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."],"supporting_citations":[{"why":"Provides the J/psi-007 differential cross sections in photon energy and momentum transfer that the two-dimensional fits use as data.","marker":"[9]"},{"why":"Supplies the holographic QCD cross-section formula, Eq. (2), relating the cross section to A_g and D_g.","marker":"[11]"},{"why":"Gives the model's fully calculated A_g and D_g shapes, which the paper replaces with a tripole form for the fit.","marker":"[16]"},{"why":"Provides the lattice QCD values of m_A, m_C, C_g(0), and the mass radius to which the extracted parameters are compared.","marker":"[19]"},{"why":"Fixes the input gluon momentum fraction A_g(0)=0.414±0.008 from a global QCD analysis.","marker":"[20]"},{"why":"Connects holographic QCD, lattice QCD, and GlueX data for nucleon mass radii, supporting the radius formula used in Eq. (4).","marker":"[22]"},{"why":"Supplies the Breit-frame formulas converting A and D into energy, pressure, and shear densities used in Section 4.","marker":"[25]"}],"fun_headline_variants":["Gluon radius of proton measured at 0.755 fm via J/psi photoproduction","J/psi near threshold reveals proton's gluon radius, matches lattice","Holographic QCD fit yields proton's gluon radius 0.755 fm","First extraction of gluon gravitational form factors from J/psi data"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"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.","fun_headline_variants_meta":{"raw":{"variants":["Gluon radius of proton measured at 0.755 fm via J/psi photoproduction","J/psi near threshold reveals proton's gluon radius, matches lattice","Holographic QCD fit yields proton's gluon radius 0.755 fm","First extraction of gluon gravitational form factors from J/psi data"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000893,"raw_usage":{"total_tokens":3875,"prompt_tokens":993,"completion_tokens":2882,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":609,"completion_tokens_details":{"reasoning_tokens":2795}},"tokens_in":609,"tokens_out":2882,"duration_ms":21111,"temperature":1.0,"reasoning_tokens":2795,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T23:00:28.450469+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"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.","supporting_citations":[],"review_version":1}