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arxiv: 2605.28285 · v1 · pith:VQJP3LFBnew · submitted 2026-05-27 · ✦ hep-ph · hep-ex

Probing hidden-charm pentaquarks from the π Nrightarrow J/psi N reaction

Samson Clymton , Sun-Young Ryu , Jung-Keun Ahn , Hyun-Chul Kim This is my paper

Pith reviewed 2026-06-29 11:48 UTC · model grok-4.3

classification ✦ hep-ph hep-ex
keywords hidden-charm pentaquarkspi N reactionJ/psi Nrescatteringcoupled-channel formalismu-channel exchangeeffective Lagrangians
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The pith

The u-channel Lambda_c exchange in pi N to J/psi N greatly enhances rescattering and produces clear peaks for Pc(4312) and Pc(4457).

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

This paper investigates whether hidden-charm pentaquarks can appear as resonances in the pi N to J/psi N reaction through dynamical generation in rescattering. It employs an off-shell coupled-channel formalism whose two-body kernels come from effective Lagrangians that include both t-channel meson exchanges and u-channel baryon exchanges. The key new element is the u-channel Lambda_c exchange, which has no counterpart in photoproduction and strongly boosts the contributions from Dbar(*) Sigma_c intermediate states. As a result the partial-wave amplitudes develop visible peaks for the Pc(4312) state with J^P = 1/2^- and the Pc(4457) state with J^P = 3/2^-, while other candidate states remain suppressed. The calculated total cross section reaches the microbarn level at these peaks.

Core claim

The u-channel Lambda_c exchange, absent in photoproduction, greatly enhances the rescattering contributions through the Dbar(*) Sigma_c intermediate states in the pi N to J/psi N reaction. This directly leads to prominent pentaquark signals where the Pc(4312) and Pc(4457) states emerge as clear peaks with J^P = 1/2^- and 3/2^- respectively, while the Pc(4380) and J^P = 5/2^- states are strongly suppressed because the Lambda_c exchange does not provide the required tensor interactions. The result for the total cross section reaches the microbarn level at the peak positions.

What carries the argument

The off-shell coupled-channel formalism whose kernels are built from effective Lagrangians that incorporate t-channel meson exchanges and u-channel baryon exchanges, with the u-channel Lambda_c term providing the decisive enhancement to the rescattering amplitudes.

If this is right

  • The Pc(4312) state appears as a clear peak with J^P = 1/2^-.
  • The Pc(4457) state appears as a clear peak with J^P = 3/2^-.
  • The total cross section reaches the microbarn level near the peak positions.
  • The Pc(4380) and 5/2^- states remain strongly suppressed.
  • The Dbar(*) Sigma_c(*) channels become comparable in size to the Dbar(*) Lambda_c channels.

Where Pith is reading between the lines

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

  • This reaction channel may therefore serve as a cleaner experimental window on the same pentaquarks than photoproduction.
  • Partial-wave analysis of future data could directly extract the J^P assignments if the peaks are observed.
  • The mechanism highlights how the choice of initial state can select which intermediate channels dominate the rescattering.

Load-bearing premise

The chosen effective Lagrangians together with the off-shell coupled-channel treatment correctly capture the dominant interaction mechanisms without missing sizable contributions that would erase or shift the predicted peaks.

What would settle it

A precision measurement of the pi N to J/psi N total or differential cross section that finds no peaks near 4312 MeV or 4457 MeV or that yields cross sections far below the microbarn level would falsify the claim of prominent signals.

Figures

Figures reproduced from arXiv: 2605.28285 by Hyun-Chul Kim, Jung-Keun Ahn, Samson Clymton, Sun-Young Ryu.

Figure 1
Figure 1. Figure 1: FIG. 1. Rescattering equations for the [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Feynman diagrams for the two-body kernel amplitudes considered in the present work: [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Summary of the results from Ref. [25] in comparison with the LHCb data [1–3, 12]. [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Total cross sections for the [PITH_FULL_IMAGE:figures/full_fig_p008_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Total cross sections of the [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Partial-wave cross sections [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. Total cross section for the [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
read the original abstract

We investigate the dynamical generation of hidden-charm pentaquark resonances in the $\pi N \to J/\psi N$ reaction utilizing an off-shell coupled-channel formalism. Motivated by the absence of pentaquark signals in $J/\psi$ photoproduction, we evaluate rescattering effects with two-body kernel amplitudes constructed from effective Lagrangians that explicitly incorporate $t$-channel meson and $u$-channel baryon exchanges. We demonstrate that the $u$-channel $\Lambda_c$ exchange, of which an analogous contribution is absent in the photoproduction kernel, greatly enhances the rescattering contributions through the $\bar{D}^{(*)}\Sigma_c$ intermediate states. Consequently, the $\bar{D}^{(*)}\Sigma_c^{(*)}$ channels yield contributions of comparable magnitude to the $\bar{D}^{(*)}\Lambda_c$ channels, directly leading to prominent pentaquark signals. The partial-wave analysis reveals that the $P_{c\bar{c}}(4312)$ and $P_{c\bar{c}}(4457)$ states emerge as clear peak structures with $J^P=1/2^-$ and $3/2^-$, respectively. In contrast, the $P_{c\bar{c}}(4380)$ and $J^P=5/2^-$ states are strongly suppressed because the $\Lambda_c$ exchange does not provide the required tensor interactions. The result for the total cross section reaches the microbarn level at the peak positions.

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 / 2 minor

Summary. The manuscript investigates the dynamical generation of hidden-charm pentaquarks in the πN → J/ψN reaction using an off-shell coupled-channel formalism. Effective Lagrangians construct the two-body kernel incorporating t-channel meson and u-channel baryon exchanges. The central result is that the u-channel Λ_c exchange (absent in photoproduction) greatly enhances rescattering through ar{D}^{(*)}Σ_c intermediate states, producing prominent peaks for P_{car{c}}(4312) with J^P=1/2^- and P_{car{c}}(4457) with 3/2^-, while P_{car{c}}(4380) and 5/2^- states are suppressed; the total cross section reaches the microbarn level at the peaks.

Significance. If the results hold, the work supplies a dynamical mechanism explaining the absence of pentaquark signals in J/ψ photoproduction while predicting observable structures in pion-induced reactions at the μb level. The explicit role of u-channel exchanges and the resulting J^P assignments add to the understanding of hidden-charm pentaquark dynamics. The standard off-shell coupled-channel construction with only two free parameters is a methodological strength that supports falsifiable predictions.

major comments (1)
  1. [numerical results and parameter discussion] The enhancement of the ar{D}^{(*)}Σ_c rescattering amplitudes and the resulting peak structures depend on the coupling constants and cutoff parameters in the effective Lagrangians (listed as free parameters in the model). The manuscript should demonstrate that the positions, heights, and visibility of the P_c peaks remain stable under reasonable variations of these parameters, as this directly affects the claim of 'prominent pentaquark signals' at the microbarn level.
minor comments (2)
  1. [partial-wave analysis] The abstract states that the Λ_c exchange 'does not provide the required tensor interactions' for the 5/2^- state; the partial-wave projection or the relevant interaction terms should be shown explicitly to support the suppression claim.
  2. [formalism] Notation for the intermediate states (ar{D}^{(*)}Σ_c vs. ar{D}^{(*)}Λ_c) and the precise definition of the off-shell form factors should be introduced with a table or equation early in the text for clarity.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive evaluation of our manuscript and for the constructive suggestion to strengthen the robustness analysis. We address the single major comment below.

read point-by-point responses

  1. Referee: [numerical results and parameter discussion] The enhancement of the ar{D}^{(*)}Σ_c rescattering amplitudes and the resulting peak structures depend on the coupling constants and cutoff parameters in the effective Lagrangians (listed as free parameters in the model). The manuscript should demonstrate that the positions, heights, and visibility of the P_c peaks remain stable under reasonable variations of these parameters, as this directly affects the claim of 'prominent pentaquark signals' at the microbarn level.

    Authors: We agree that an explicit demonstration of stability under parameter variation would strengthen the claims. The pole positions themselves are fixed by the coupled-channel dynamics and remain stable, but the absolute heights of the cross-section peaks depend on the two free cutoff parameters (and on the overall normalization of the couplings, which are constrained by SU(4) relations). In the revised manuscript we will add a dedicated subsection (and an accompanying figure) showing the total cross section for cutoff variations of ±20 % around the central values used in the paper. This will confirm that the microbarn-scale peaks for the 1/2^- and 3/2^- states remain visible and that the suppression of the other states is preserved. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation self-contained

full rationale

The paper builds an off-shell coupled-channel model from effective Lagrangians that include explicit t-channel meson and u-channel baryon exchanges. The central result—that u-channel Λc exchange enhances Dbar(*)Σc rescattering and produces visible peaks at the quoted Pc masses and J^P values—follows from solving the coupled equations with that kernel term present. The abstract and description indicate only two free parameters and no load-bearing self-citation, self-definition of outputs in terms of inputs, or renaming of fitted quantities as predictions. The enhancement is a calculational consequence of the model choice, not a reduction by construction. This is the normal case of an independent model prediction.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on effective Lagrangians whose couplings and cutoffs are free parameters, plus standard assumptions of unitarity and effective theory validity in the relevant energy range; no new entities are postulated beyond the pentaquarks already reported by LHCb.

free parameters (2)
  • coupling constants
    Strengths of meson and baryon exchanges in the effective Lagrangians are adjusted parameters.
  • cutoff parameters
    Regularization scales in the off-shell integrals are chosen to control divergences.
axioms (2)
  • domain assumption Effective Lagrangians capture low-energy hadron interactions
    Invoked when constructing the two-body kernel amplitudes from t- and u-channel exchanges.
  • standard math Coupled-channel equations enforce unitarity
    Used in the off-shell formalism to generate the rescattering amplitudes.

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discussion (0)

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Reference graph

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