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arxiv: 2601.12778 · v2 · pith:SMN6RWQGnew · submitted 2026-01-19 · ✦ hep-ph

Search for the low-lying excited baryon Sigma^*(1/2^-) through process Λ^+_c to Λ K⁰ π^+

Sheng-Chao Zhang , Wen-Tao Lyu , Guan-Ying Wang , Bo-Qiang Ma , En Wang This is my paper

Pith reviewed 2026-05-22 12:28 UTC · model grok-4.3

classification ✦ hep-ph
keywords Sigma* resonanceLambda_c decayinvariant mass distributiondynamical generationBESIII experimentexcited baryonslight baryon spectrum
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0 comments X

The pith

A model of Λ_c^+ → Λ K^0 π^+ decay predicts a cusp at 1.43 GeV from the low-lying Σ*(1/2^-) baryon.

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

This paper examines the singly Cabibbo-suppressed decay of the charmed baryon Λ_c^+ into Λ K^0 π^+ to search for a low-lying excited state called Σ*(1/2^-). The authors include this state as dynamically generated from S-wave interactions of pseudoscalar mesons with octet baryons, along with known resonances K*(892) and N(1535). Their calculation matches the BESIII data on the π^+ K^0 invariant mass distribution. It further predicts a noticeable cusp near 1.43 GeV in the π^+ Λ distribution that would indicate the presence of this new state. High-precision experiments at facilities like BESIII and Belle II could confirm or rule out this prediction and refine our picture of light baryon resonances.

Core claim

Incorporating the contribution from the dynamically generated Σ*(1/2^-) resonance via S-wave pseudoscalar meson-octet baryon interactions, in addition to the K*(892) and N(1535) intermediates, the model reproduces the experimental π^+ K^0 invariant mass spectrum and generates a distinct cusp structure around 1.43 GeV in the π^+ Λ invariant mass distribution associated with the Σ*(1/2^-).

What carries the argument

The Σ*(1/2^-) resonance dynamically generated in the S-wave pseudoscalar meson-octet baryon channel, which produces the predicted cusp through its contribution to the decay amplitude.

If this is right

  • The model reproduces the BESIII π^+ K^0 invariant mass distribution.
  • A distinct cusp structure appears around 1.43 GeV in the π^+ Λ invariant mass distribution.
  • Future high-precision measurements at BESIII, Belle II, and Super Tau-Charm Facility can test the existence of the Σ*(1/2^-).

Where Pith is reading between the lines

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

  • Confirmation of the cusp would connect charmed baryon decays to tests of dynamical generation for light baryon states.
  • The same framework could be applied to related decay modes to map additional features in the baryon spectrum.
  • Absence of the cusp in new data would require revisiting the modeling assumptions for this resonance.

Load-bearing premise

The low-lying excited baryon Σ*(1/2^-) exists as a dynamically generated state from S-wave pseudoscalar meson-octet baryon interactions and produces a visible cusp in the invariant mass distribution.

What would settle it

A precise measurement of the π^+ Λ invariant mass distribution in Λ_c^+ → Λ K^0 π^+ that lacks any cusp feature near 1.43 GeV.

Figures

Figures reproduced from arXiv: 2601.12778 by Bo-Qiang Ma, En Wang, Guan-Ying Wang, Sheng-Chao Zhang, Wen-Tao Lyu.

Figure 1
Figure 1. Figure 1: FIG. 1: Feynman diagram at the quark level for the [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Mechanisms for the process Λ [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Mechanisms for the Λ [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: The [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6: Dalitz plots of “ [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
read the original abstract

Motivated by recent BESIII measurements of the singly Cabibbo-suppressed processes $\Lambda^+_c \to \Lambda K^+ \pi^0$ and $\Lambda^+_c \to \Lambda K_S^0 \pi^+$, we investigate the process $\Lambda^+_c \to \Lambda K^0 \pi^+$ by taking into account the contribution from the low-lying excited baryon $\Sigma^*(1/2^-)$, dynamically generated via the $S$-wave pseudoscalar meson-octet baryon interaction, as well as from the intermediate resonances $K^*(892)$ and $N(1535)$. Our model successfully reproduces the BESIII $\pi^+K^0$ invariant mass distribution, and predicts a distinct cusp structure around 1.43~GeV in the $\pi^+\Lambda$ invariant mass distribution, which is associated with the predicted $\Sigma^*(1/2^-)$. Future high-precise measurements of this process at BESIII, Belle~II, and the proposed Super Tau-Charm Facility experiments will be crucial for testing the existence of $\Sigma^*(1/2^-)$ and advancing our understanding of the light baryon spectrum.

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

2 major / 2 minor

Summary. The manuscript investigates the singly Cabibbo-suppressed decay Λ_c^+ → Λ K^0 π^+ by constructing an amplitude that includes the dynamically generated Σ*(1/2^-) resonance (from S-wave pseudoscalar meson-octet baryon interactions), together with intermediate K*(892) and N(1535) contributions. The central claims are that the model reproduces the BESIII π^+ K^0 invariant-mass distribution and predicts a distinct cusp near 1.43 GeV in the π^+ Λ invariant-mass spectrum as a signature of the Σ*(1/2^-).

Significance. If the predicted cusp is confirmed by future high-statistics data, the work would furnish a testable signature for the low-lying Σ*(1/2^-) in a new decay channel and thereby strengthen the case for its dynamical generation within chiral-unitary frameworks. The reported reproduction of existing BESIII data provides a non-trivial consistency check, but the overall impact remains conditional on experimental verification of the specific structure.

major comments (2)
  1. [Abstract and §3 (amplitude construction)] Abstract and model section: the claim of successful reproduction of the BESIII π^+ K^0 invariant mass distribution is stated without supplying the numerical values of the free parameters (cutoff or subtraction constants), the explicit fit procedure, χ² values, or error bands. This absence makes it impossible to judge whether the reproduction is robust or merely qualitative.
  2. [§2 (resonance input) and §4 (results)] Theoretical framework: the Σ*(1/2^-) pole position and its coupling to the πΛ channel are imported directly from earlier dynamical-generation calculations; the cusp at ~1.43 GeV is therefore a built-in feature of the input resonance rather than an independent prediction generated within the present amplitude. This reduces the novelty of the test for the resonance’s existence.
minor comments (2)
  1. [Title and abstract] The title uses K^0 while the abstract and text refer to both K^0 and K_S^0; a brief clarification of the isospin relation and experimental tagging would improve readability.
  2. [Figure 2 and Figure 3] Figure captions for the invariant-mass distributions should explicitly state the binning, normalization, and whether the curves include interference terms or only the resonant contributions.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of the manuscript and the constructive comments. We address each major comment below and indicate the changes made to the revised version.

read point-by-point responses

  1. Referee: [Abstract and §3 (amplitude construction)] Abstract and model section: the claim of successful reproduction of the BESIII π^+ K^0 invariant mass distribution is stated without supplying the numerical values of the free parameters (cutoff or subtraction constants), the explicit fit procedure, χ² values, or error bands. This absence makes it impossible to judge whether the reproduction is robust or merely qualitative.

    Authors: We agree that the original manuscript lacked sufficient detail on the numerical inputs and fit quality. In the revised version we now explicitly list the cutoff value and subtraction constants used in the chiral-unitary amplitude, describe the fitting procedure to the BESIII π^+ K^0 distribution, report the obtained χ², and display theoretical error bands on the corresponding figure. revision: yes

  2. Referee: [§2 (resonance input) and §4 (results)] Theoretical framework: the Σ*(1/2^-) pole position and its coupling to the πΛ channel are imported directly from earlier dynamical-generation calculations; the cusp at ~1.43 GeV is therefore a built-in feature of the input resonance rather than an independent prediction generated within the present amplitude. This reduces the novelty of the test for the resonance’s existence.

    Authors: The pole position is indeed taken from prior chiral-unitary work, as is standard when testing a resonance in a new channel. The novelty of the present study lies in the construction of the full decay amplitude for Λ_c^+ → Λ K^0 π^+ that consistently includes the Σ*(1/2^-), K*(892) and N(1535) contributions, and in the resulting prediction of a visible cusp specifically in the π^+ Λ invariant-mass spectrum. This constitutes a new, experimentally testable signature in a decay mode not previously examined for this resonance. revision: no

Circularity Check

0 steps flagged

No significant circularity: standard chiral-unitary amplitude applied to new decay channel

full rationale

The derivation constructs a decay amplitude that incorporates the Σ*(1/2^-) pole position and couplings obtained from prior S-wave meson-baryon scattering calculations, together with K*(892) and N(1535) contributions. This amplitude is then used to reproduce the measured π⁺K⁰ invariant-mass spectrum and to compute the π⁺Λ spectrum, where a cusp appears at the resonance location. Because the resonance parameters are fixed by the scattering sector (independent of the present decay data) and the new observable is a distinct final-state distribution, the prediction does not reduce to a re-statement of the input by construction. No self-definitional loop, fitted parameter renamed as prediction, or load-bearing self-citation chain is required for the central claim.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 1 invented entities

The central claim rests on the validity of the chiral unitary approach for generating the Σ* pole and on the assumption that its contribution dominates the predicted cusp structure.

free parameters (1)
  • model cutoff or subtraction constants
    Standard parameters in chiral unitary models that are adjusted to reproduce resonance poles or data.
axioms (1)
  • domain assumption The Σ*(1/2⁻) is dynamically generated from S-wave pseudoscalar meson-octet baryon interaction.
    Invoked in the abstract as the source of the resonance contribution to the decay amplitude.
invented entities (1)
  • Σ*(1/2⁻) no independent evidence
    purpose: To produce the predicted cusp in the π⁺Λ invariant mass distribution.
    Postulated resonance whose existence is assumed from prior work and tested via the new observable.

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Probing the isospin structure and low-lying resonances in $\Lambda_c^+ \to n\bar{K}^0 \pi^+$ decays

    hep-ph 2026-02 unverdicted novelty 5.0

    The chiral unitary calculation predicts a narrow peak from N(1535) in the pi+ n invariant mass spectrum and a dip from Lambda(1670) in the K0bar n spectrum, supporting the molecular interpretation of these resonances.

Reference graph

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