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arxiv: 2607.02485 · v1 · pith:OTNQEHZ4new · submitted 2026-07-02 · ✦ hep-ph

Identifying Sigma(1380) and Sigma(1430) in the J/psi to Λ π bar{Sigma} reaction

Wen-Tao Lyu , Eulogio Oset , De-Min Li , En Wang This is my paper

Pith reviewed 2026-07-03 09:24 UTC · model grok-4.3

classification ✦ hep-ph
keywords Sigma resonancesJ/psi decayspi Lambda interactionpi Sigma-bar interactionresonance identificationbaryon spectroscopy
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0 comments X

The pith

The π Σ-bar interaction accounts for the low-energy spectrum in J/ψ → Λ π Σ-bar without needing the Σ(1380).

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

The paper analyzes the J/ψ → Λ π Σ-bar reaction by examining the π+ Λ mass distribution at low energies to search for signals of low-lying Σ+ states. It identifies a clear peak for the Σ(1385) (3/2+) and a smaller one for the Σ(1430) (1/2-). An initial fit using only the πΛ interaction requires both the Σ(1430) and the predicted Σ(1380) (1/2-) to match the data. When the π Σ-bar interaction is added to the model, the spectrum is reproduced without the Σ(1380), indicating that the earlier need for this state arose from an incomplete treatment of the coupled channels.

Core claim

In the J/ψ → Λ π Σ-bar reaction, the πΛ mass distribution shows the established Σ(1385) and the Σ(1430). A model limited to the πΛ interaction requires an additional Σ(1380) contribution to fit the low-energy region, but extending the model to include the π Σ-bar interaction removes any need for the Σ(1380) while still accounting for the observed spectrum.

What carries the argument

The coupled πΛ and π Σ-bar interactions in a theoretical model that generates the low-lying Σ resonances and their contributions to the invariant mass distribution.

If this is right

  • The Σ(1380) is not required to explain the low-energy part of the πΛ spectrum once the π Σ-bar channel is included.
  • The Σ(1430) appears as a distinct 1/2- contribution in this reaction.
  • Multi-channel interactions must be considered to avoid spurious resonance signals in baryon spectroscopy.

Where Pith is reading between the lines

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

  • Claims for the Σ(1380) from earlier experiments may need re-examination using coupled-channel models that include the π Σ-bar interaction.
  • Data on the π Σ-bar mass distribution in the same or related reactions could test whether the model without Σ(1380) continues to hold.
  • Similar coupled-channel analyses could clarify the status of other disputed low-lying Σ states in different production mechanisms.

Load-bearing premise

The theoretical model for the πΛ and π Σ-bar interactions accurately describes the low-energy dynamics without missing contributions from other channels or effects.

What would settle it

A measurement of the π Σ-bar invariant mass spectrum or a refined fit that still requires an explicit Σ(1380) pole to match the data even after including the full πΛ–π Σ-bar interaction.

Figures

Figures reproduced from arXiv: 2607.02485 by De-Min Li, En Wang, Eulogio Oset, Wen-Tao Lyu.

Figure 1
Figure 1. Figure 1: FIG. 1. Diagrammatic representation of the [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. The [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. (a) Tree level in [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. The [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. The [PITH_FULL_IMAGE:figures/full_fig_p006_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: We call ⃗pi the momenta in the J/ψ rest frame and θ J/ψ π + (2) Λ (1) Σ¯ − (3) FIG. 8. Particles in J/ψ → Λπ +Σ¯ − in the 1, 2 rest frame. p⃗˜i the momenta in the 1, 2 rest frame. Note that we go from the J/ψ rest frame to the 1, 2 rest frame by making a boost along the direction of ⃗pΣ¯− (3) and opposite sign. Note also that in the 1, 2 rest frame p⃗˜J/ψ = p⃗˜Σ¯− . (A3) We define as θ angle the one of par… view at source ↗
read the original abstract

We study the $J/\psi \to \Lambda \pi \bar{\Sigma}$ reaction by looking at the $\pi^+ \Lambda$ mass distribution at low energies, in search of signals for the low lying $\Sigma^+$ states. Apart from a clear signal of the $\Sigma(1385) (3/2^+)$ state, we find a smaller peak for the predicted $\Sigma(1430) (1/2^-)$, which has already been confirmed by the Belle Collaboration. A first analysis, considering only the $\pi\Lambda$ interaction, shows that the low energy part of the spectrum is better reproduced including contributions from the $\Sigma(1430)$ and the predicted $\Sigma(1380)(1/2^-)$ state that has been claimed before from analyses of different experiments. However, when we consider the $\pi\bar{\Sigma}$ interaction the need for the $\Sigma(1380)$ disappears.

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 / 0 minor

Summary. The manuscript studies the J/ψ → Λ π ar{Σ} reaction by analyzing the low-energy π⁺Λ mass distribution to search for signals of low-lying Σ⁺ states. It reports a clear Σ(1385)(3/2⁺) signal, a smaller peak consistent with the Σ(1430)(1/2⁻) previously seen by Belle, and finds that an initial fit using only the πΛ interaction requires both the Σ(1430) and the controversial Σ(1380)(1/2⁻); however, once the πar{Σ} interaction is included, the Σ(1380) contribution is no longer needed.

Significance. If the coupled-channel amplitudes are shown to be complete and the fit improvement is quantitatively documented, the result would provide a concrete dynamical explanation for the apparent Σ(1380) signal in this channel and help clarify the low-lying Σ spectrum. The work directly addresses a long-standing question about whether Σ(1380) is required by data or is an artifact of incomplete modeling.

major comments (1)
  1. [Abstract] Abstract (and the central claim): the statement that 'when we consider the πar{Σ} interaction the need for the Σ(1380) disappears' is load-bearing for the paper's main conclusion, yet no quantitative measure (χ² per degree of freedom, Δχ² when the resonance is removed, or residual plots) is supplied to demonstrate that the improvement is due to the added channel rather than parameter adjustment. This directly engages the completeness assumption highlighted in the stress-test note.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed reading and the constructive comment on the quantitative support for our central claim. We agree that the abstract statement requires explicit numerical backing to demonstrate that the πΣ-bar channel, rather than parameter freedom, accounts for the disappearance of the Σ(1380) contribution. We will revise the manuscript to include the requested measures and a short discussion of model assumptions.

read point-by-point responses

  1. Referee: [Abstract] Abstract (and the central claim): the statement that 'when we consider the πΣ-bar interaction the need for the Σ(1380) disappears' is load-bearing for the paper's main conclusion, yet no quantitative measure (χ² per degree of freedom, Δχ² when the resonance is removed, or residual plots) is supplied to demonstrate that the improvement is due to the added channel rather than parameter adjustment. This directly engages the completeness assumption highlighted in the stress-test note.

    Authors: We accept the point. The current abstract and text do not report χ²/dof values or Δχ² for the fits with versus without the Σ(1380) once the πΣ-bar channel is included. In the revised manuscript we will add these numbers (both for the πΛ-only and the coupled-channel cases), together with a brief statement on the number of free parameters in each fit. We will also include a short paragraph addressing the completeness of the coupled-channel amplitudes, noting that they are taken from the chiral unitary framework already tested against multiple data sets in our prior works. Residual plots will be added to the supplementary material if space is limited in the main text. revision: yes

Circularity Check

0 steps flagged

No significant circularity; central result follows from explicit channel comparison

full rationale

The paper models the J/ψ → Λ π Σ-bar reaction using amplitudes for πΛ and π Σ-bar scattering derived from chiral unitary approaches. It first fits the πΛ-only case, finding that both Σ(1430) and Σ(1380) improve the low-energy spectrum description. Upon adding the π Σ-bar channel, the Σ(1380) contribution is no longer required to reproduce the data. This outcome is obtained by direct comparison of the two model variants against the same mass distribution; it is not obtained by redefining the resonance parameters or by fitting a quantity that is already fixed by the input amplitudes. Prior predictions of the Σ(1380) and Σ(1430) are cited as external motivation for testing their presence, but the load-bearing step (the disappearance upon channel inclusion) is an independent numerical result of the coupled-channel calculation and does not reduce to a self-citation or to a tautological re-labeling of the fit. The derivation chain therefore remains self-contained against the external benchmark of the measured spectrum.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract only; no explicit free parameters, axioms, or invented entities are described.

pith-pipeline@v0.9.1-grok · 5715 in / 1037 out tokens · 35866 ms · 2026-07-03T09:24:11.840503+00:00 · methodology

discussion (0)

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