Pith. sign in

REVIEW 3 major objections 5 minor 58 references

This paper reports the first measurement of the sine of the relative phase between the proton's psionic (time-like) form factors, sin ΔΦ = −0.20 ± 0.34 (stat) ± 0.11 (syst), obtained from the normal polarization of the proton in e⁺e⁻ → J/ψ

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

T0 review · deepseek-v4-flash

2026-08-01 11:12 UTC pith:6WWWA4EK

load-bearing objection A genuine first measurement — the proton psionic form-factor phase — but the headline number is consistent with zero, and the paper's soft spot is the analyzing-power calibration, not the statistics. the 3 major comments →

arxiv 2607.19948 v1 pith:6WWWA4EK submitted 2026-07-22 hep-ex

First Measurement of the Relative Phase between Proton Psionic Form Factors

BESIII Collaboration: M. Ablikim , M. N. Achasov , P. Adlarson , X. C. Ai , C. S. Akondi , R. Aliberti , A. Amoroso , Q. An
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Y. H. An Y. Bai O. Bakina Y. Ban H.-R. Bao X. L. Bao V. Batozskaya K. Begzsuren N. Berger M. Berlowski M. B. Bertani D. Bettoni F. Bianchi E. Bianco A. Bortone I. Boyko R. A. Briere A. Brueggemann H. Cai M. H. Cai X. Cai A. Calcaterra G. F. Cao N. Cao S. A. Cetin X. Y. Chai J. F. Chang T. T. Chang G. R. Che Y. Z. Che C. H. Chen Chao Chen G. Chen H. S. Chen H. Y. Chen M. L. Chen S. J. Chen S. M. Chen T. Chen W. Chen X. R. Chen X. T. Chen X. Y. Chen Y. B. Chen Y. Q. Chen Z. K. Chen J. Cheng L. N. Cheng S. K. Choi X. Chu G. Cibinetto F. Cossio J. Cottee-Meldrum H. L. Dai J. P. Dai X. C. Dai A. Dbeyssi R. E. de Boer D. Dedovich C. Q. Deng Z. Y. Deng A. Denig I. Denisenko M. Destefanis F. De Mori X. X. Ding Y. Ding Y. X. Ding Yi. Ding J. Dong L. Y. Dong M. Y. Dong X. Dong M. C. Du S. X. Du Shaoxu Du X. L. Du Y. Q. Du Y. Y. Duan Z. H. Duan P. Egorov G. F. Fan J. J. Fan Y. H. Fan J. Fang Jin Fang S. S. Fang W. X. Fang Y. Q. Fang L. Fava F. Feldbauer G. Felici C. Q. Feng J. H. Feng L. Feng Q. 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This is my paper
classification hep-ex PACS 13.40.Gp13.88.+e14.20.Dh
keywords proton form factorspsionic form factorsrelative phasepolarizationJ/psi decaye+e- annihilationsecondary scatteringanalyzing power
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper aims to establish the first measurement of the relative phase between the proton's electric and magnetic form factors in the time-like region, specifically for J/ψ decay, where they are called psionic form factors. This phase had remained unmeasured because it requires determining the polarization of the final-state proton, a formidable experimental challenge. The authors exploit a novel technique: protons produced in e⁺e⁻ → J/ψ → p p̄ scatter elastically off hydrogen nuclei in the detector's beam pipe, and the azimuthal asymmetry of that secondary scattering reveals the proton's polarization. An unbinned maximum-likelihood fit to 2556 such events yields sin ΔΦ = −0.20 ± 0.34 (stat) ± 0.11 (syst), the first direct constraint on this quantity. If correct, this result offers new insight into proton formation dynamics and provides a data point for testing SU(3) symmetry across the baryon octet.

Core claim

The central claim is that the sine of the relative phase ΔΦ between the psionic electric and magnetic form factors of the proton can be extracted from the normal polarization P_y of the proton in e⁺e⁻ → J/ψ → p p̄, and that P_y can be measured without a dedicated polarimeter by using the detector's own material: protons that scatter elastically off hydrogen in the mineral-oil layer of the beam pipe produce a spin-dependent azimuthal asymmetry proportional to P_y A_N(θ), where A_N(θ) is the empirically known analyzing power for proton-proton scattering. Fitting the azimuthal distribution of the scattering events yields sin ΔΦ = −0.20 ± 0.34 (stat) ± 0.11 (syst). This is the first direct deter

What carries the argument

The central object is the normal polarization P_y of the final-state proton, related to the relative phase by P_y = sqrt(1−α²) cosθ_p sinθ_p sinΔΦ / (1 + α cos²θ_p), where α is the J/ψ → p p̄ decay parameter. P_y is measured through the azimuthal asymmetry of elastic proton-proton scattering: dσ/dϕ ∝ 1 + P_y A_N(θ) cosϕ, where A_N(θ) is the proton-proton analyzing power. The detector itself becomes a proton polarimeter: the beam-pipe oil layer serves as a hydrogen target, and the fit extracts sinΔΦ directly from the ϕ distribution.

Load-bearing premise

The extraction assumes that the empirical proton-proton analyzing power A_N(θ) exactly describes scattering off hydrogen in the beam-pipe oil layer, and that the up-to-7.7% of quasi-free nuclear collisions contribute zero analyzing power; if either fails, the inferred sin ΔΦ shifts.

What would settle it

A measurement of the sideways polarization P_x (requiring a polarized beam) or of the antiproton polarization would resolve the two ΔΦ solutions and check the sign; a higher-statistics measurement of P_y with a known analyzing power—or a direct measurement of the asymmetry of events assigned to quasi-free collisions—would expose any bias from the assumed A_N.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

If this is right

  • Provides the first experimental constraint on the relative phase of proton psionic form factors, a quantity needed for a complete description of the proton's internal structure.
  • Offers a test of SU(3) flavor symmetry by comparing the proton's phase with those already measured for hyperons in J/ψ decay.
  • Validates the technique of using detector material as a proton polarimeter, which can be applied to other final states and other baryons.
  • The result leaves a two-fold ambiguity in ΔΦ, to be resolved by measuring an additional polarization observable such as P_x with a polarized beam.
  • If confirmed, the near-zero central value suggests the phase is small, providing a data point that nucleon-structure models must reproduce.

Where Pith is reading between the lines

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

  • If the technique is sound, it could be extended to neutron final states using neutron scattering off hydrogen or carbon, enabling the neutron psionic form-factor phase to be measured at the same facility.
  • The same secondary-scattering approach could be applied to ψ(2S) → p p̄ to check whether the phase is process-dependent, testing the assumption that psionic form factors are universal.
  • The systematic uncertainty is dominated by the unknown analyzing power of quasi-free nuclear collisions; a dedicated measurement of that contribution would sharpen the result more than simply increasing statistics.
  • A future high-luminosity measurement could turn this first glance into a precision test: if the true phase is near the current central value, models that predict large phases would be disfavored.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. This Letter reports the first measurement of the sine of the relative phase ΔΦ between the electric and magnetic psionic (J/ψ-decay) form factors of the proton. Using 10.09×10⁹ J/ψ events at BESIII, the collaboration selects 2556 e+e−→J/ψ→p p̄ events in which the final-state proton rescatters elastically off hydrogen in the beam-pipe mineral-oil layer or the MDC inner wall, and exploits the azimuthal asymmetry dσ/dφ ∝ 1 + P_y A_N(θ)cosφ with A_N taken from the SAID database. An unbinned maximum-likelihood fit to W ∝ (1+α cos²θ_p)(1+P_y A_N cosφ), with α_J/ψ fixed to 0.595 from a previous BESIII measurement, yields sinΔΦ = −0.20 ± 0.34_stat ± 0.11_syst. The result is consistent with zero and is the first direct constraint on this observable; it is placed in the context of the baryon-octet pattern. A single pseudo-experiment (input −0.84, output −0.82±0.02) and a systematic table are provided.

Significance. If the number holds, this is the first determination of a long-sought observable and a proof of principle for a novel polarimeter concept: using the beam pipe of a general-purpose spectrometer as a proton polarimeter. The analysis is careful and transparent: unbinned likelihood with MC normalization, control-sample efficiency corrections, an explicit systematic table, and an honestly statistics-dominated uncertainty. The extraction is not circular — α_J/ψ [23] and A_N [49] are external inputs. As a first measurement, the result is genuinely useful for nucleon-structure models and for planning future facilities. The principal weakness is the absolute calibration of the polarimeter: the 2% analyzing-power uncertainty is asserted, not supported, and the validation pseudo-experiment does not test the external A_N scale. I estimate, however, that a 10% A_N scale error would shift the central value by only ~0.02–0.04 because |sinΔΦ|≈0.2, so the qualitative conclusion (consistency with zero, statistics-dominated errors) is robust; the issue affects the rigor of the quoted systematic rather than the main physics statement. The stress-test claim that a 10% miscalibration shifts the result b

major comments (3)
  1. [Systematic uncertainties / Table I ('Analyzing power'); Eq. (2)] The 2% uncertainty assigned to A_N is asserted without support, and no in-situ calibration of the oil-target polarimeter is shown: the pseudo-experiment (input −0.84, output −0.82±0.02) re-uses the same A_N in generation and fitting, so it validates the fitter, not the external scale of Eq. (2). Since sinΔΦ is inversely proportional to the assumed A_N, scale errors propagate directly into the central value; for the measured size, a 10% miscalibration shifts sinΔΦ by ~0.02–0.04, exceeding the assigned 0.009 and rivaling the other Table I entries. Please calibrate with protons of known polarization (e.g., Λ→pπ−) from the same dataset, or propagate the SAID uncertainty (scatter of partial-wave solutions in Ref. [49]), or quote the shift for ±5%/±10% variations and enlarge the systematic.
  2. [Fit (Eq. 3) and Table I] The fit fixes α_J/ψ = 0.595 from Ref. [23], but Table I lists no systematic for the uncertainty of this external input. Eq. (1) couples α to sinΔΦ through √(1−α²) and the denominator 1+α cos²θ_p; d ln sinΔΦ/dα ≈ −1.2, so δα ≈ 0.03–0.05 gives a shift ≈ 0.01, comparable to the 'Fit method' entry 0.010. Add a Table I entry from varying α within its published uncertainty, or justify neglect quantitatively.
  3. [Systematic uncertainties ('Quasi-free collision'); Table I] The treatment of quasi-free collisions is conservative in direction: with A_N ≥ 0 for quasi-free events, setting A_N = 0 (and using the upper-bound fraction 7.7%) brackets the dilution bias. However, the text should say so explicitly, because Table I sums this worst-case bound in quadrature with entries defined by 'most significant difference' (mass window 0.040, momentum requirement 0.049), which are not 1σ estimates. Mixing conservative bounds and 1σ estimates in a quadrature sum is nonstandard; either report the bound separately or convert all entries to a common definition. Also state how the 7.7% fraction and its uncertainty were determined.
minor comments (5)
  1. [Validation pseudo-experiment (text near Eq. 4)] Only a single pseudo-experiment is described ('we obtain sinΔΦ = −0.82±0.02'); the deviation from input is one standard deviation of that run. The 'Fit method' entry (0.010) should be derived from the pull distribution of an ensemble of pseudo-experiments, not a single run; specify the ensemble size and the quoted pull width.
  2. [Background statement, §Systematics] The text says the ~0.5% background is 'considered in the systematic uncertainty evaluation', but no Table I row corresponds to it. State which entry covers the background (mass window? fit method?) and how it enters.
  3. [Fig. 6 and discussion] With σ ≈ 0.34, the proton is consistent at ≲1.5σ with all octet values; the statement that the proton phase is 'close to Σ+/0 and smaller than Λ and Ξ−/0' is not supported at this precision. Soften to 'consistent with' and quote the significances of the differences.
  4. [Notation; abstract vs. text] Eq. (2)/Fig. 1 use θ, φ for the pp scattering (θ in the pp c.m. frame per Fig. 4 caption), while θ_p is the J/ψ-frame angle; the text switches between them, so state the frames explicitly. Also, the abstract quotes 10.09×10⁹ J/ψ events while the text uses 10×10⁹ (Ref. [38]); harmonize.
  5. [Spin precession paragraph] The correction is described qualitatively ('rotate the coordinate system'). Report the typical precession angle (~1–2° for the two target radii, if my estimate is right) and any residual systematic; this is a novel aspect of the technique and deserves a number.

Circularity Check

0 steps flagged

No significant circularity: sinΔΦ is a free parameter fitted to data using external inputs (α_J/ψ and A_N); no equation reduces the target to its inputs.

full rationale

The extraction chain is not circular. The target parameter sinΔΦ appears explicitly as the free parameter in the unbinned maximum-likelihood fit, Eq. (3): W ∝ (1+α_J/ψ cos²θ_p)(1+P_y A_N(θ) cosφ), with P_y related to sinΔΦ by Eq. (1). Nothing in the construction fixes sinΔΦ from the inputs: α_J/ψ = 0.595 is taken from a previous BESIII measurement (Ref. [23]) of the J/ψ→p pbar angular distribution, and A_N is taken from the external SAID database (Ref. [49]); neither is fitted to, or derived from, the azimuthal asymmetry that determines sinΔΦ. The pseudo-experiment (input −0.84, output −0.82±0.02) tests internal consistency, but the result remains a measurement, not a prediction forced by construction. The cited validation of the polarimeter technique (Ref. [37]) is an independent prior study; citing it is ordinary self-citation rather than load-bearing circularity. Concerns about the transfer of SAID analyzing powers to the oil-target protons are external-calibration or systematic-uncertainty questions, not circularity of the derivation.

Axiom & Free-Parameter Ledger

1 free parameters · 6 axioms · 0 invented entities

No new particles, forces, or conserved quantities are introduced. The analysis rests on standard QED/QCD-inspired form-factor formalism, external inputs (α_J/ψ and SAID A_N), and the assumption that the detector simulation faithfully reproduces the secondary-scattering and spin-precession physics.

free parameters (1)
  • α_J/ψ (decay parameter) = 0.595 (fixed, from BESIII [23])
    Fixed in the likelihood fit rather than measured here. It enters Eq. (1) and converts the measured P_y into sinΔΦ. Its uncertainty is not propagated in the systematic table.
axioms (6)
  • domain assumption Eq. (1): P_y = sqrt(1-α²) cosθ_p sinθ_p sinΔΦ / (1+α cos²θ_p)
    Standard two-form-factor formalism for J/ψ→p pbar, cited to Refs. [14,21,22]; assumed valid for the extraction.
  • domain assumption Eq. (2): dσ/dφdcosθ ∝ 1 + P_y A_N(θ) cosφ
    Spin-dependent pp elastic scattering formalism from Refs. [24,25]; assumed valid for protons scattering on hydrogen in the beam-pipe oil layer.
  • domain assumption SAID pp analyzing power database is accurate at the relevant proton momenta
    A_N(θ) is taken event-by-event from SAID [49]; the paper assigns only a 2% uncertainty for potential variations.
  • domain assumption α_J/ψ = 0.595 from BESIII [23]
    External input used without propagating its uncertainty into the quoted systematic error.
  • domain assumption Geant4 simulation correctly models detector response, spin precession, and secondary scattering
    Used for efficiency, signal MC, validation, and the spin-precession rotation correction; not independently verifiable from the paper.
  • domain assumption Target protons in the oil layer are effectively free and at rest after the |p_target| < 50 MeV/c cut
    The cut suppresses quasi-free nuclear collisions; if residual nuclear motion or binding effects remain, the pp scattering kinematics and analyzing-power assumption could be biased.

pith-pipeline@v1.3.0-alltime-deepseek · 22764 in / 12318 out tokens · 128758 ms · 2026-08-01T11:12:11.823460+00:00 · methodology

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read the original abstract

The relative phase between the time-like form factors of the proton is a crucial observable for a complete understanding of its internal structure, yet it has remained unmeasured due to the formidable experimental challenge of determining the final-state polarization or having available polarized beams. With a novel technique that measures polarization via secondary scattering on spectrometer material, we use $10.09\times10^{9}$ $J/\psi$ events collected at BESIII to analyze the reaction $e^+e^-\rightarrow J/\psi \rightarrow p\bar{p}$. This allows the first determination of the sine of the relative phase between the proton psionic form factors, $\sin\Delta\Phi=-0.20\pm0.34_{\textrm{stat}}\pm0.11_{\textrm{syst}}$. This result provides the first direct insight into the complex dynamics of proton formation, and offers valuable new information to constrain theoretical models of nucleon structure.

Figures

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Figure 1
Figure 1. Figure 1: FIG. 1. Schematic of the reaction [PITH_FULL_IMAGE:figures/full_fig_p006_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Distribution of [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Polar angle distribution of the scattered proton in [PITH_FULL_IMAGE:figures/full_fig_p008_4.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Distributions of [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Distributions of the azimuthal angle [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Relative phase of form factors for baryon octet states. [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗

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