arxiv: 2605.00727 · v1 · submitted 2026-05-01 · ⚛️ nucl-th

Recognition: unknown

Hyperon-nucleon interaction through the K^-dtoπΛ N reaction

Shunsuke Yasunaga , Daisuke Jido

Authors on Pith no claims yet

Pith reviewed 2026-05-09 18:21 UTC · model grok-4.3

classification ⚛️ nucl-th

keywords hyperon-nucleon interactionfinal-state interactioncoupled-channelK-matrixinvariant mass spectrumSigma N thresholdLambda pK- d reaction

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The pith

The Λp invariant mass spectrum in the K^-d to π^-Λp reaction shows threshold structures sensitive to the ΛN-ΣN coupled-channel interaction.

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

The paper studies the hyperon-nucleon force by looking at how the Λ and nucleon particles interact after being produced in the reaction of a K- meson with a deuteron. It centers on the coupled ΛN and ΣN channels, which generate visible features in the Λp pair's invariant mass distribution right at the ΣN threshold energies. A K-matrix model built from scattering lengths in isospin channels describes the conversion process, and calculations reveal that the detailed shape of these features changes with the sign and size of the I=1/2 scattering length. Adding simple background processes still leaves the structures intact but alters their exact form, so the spectrum itself becomes a practical way to pin down the unknown details of the hyperon-nucleon forces.

Core claim

The spin-triplet ΣN to Λp conversion amplitude, constructed in the K-matrix formalism from isospin-basis scattering lengths, produces characteristic structures around the ΣN thresholds in the Λp invariant mass spectrum of the K^-d → π^-Λp reaction. These structures vary with the choice of ΣN scattering lengths, especially the sign of the real part of the I=1/2 length, and remain visible after background diagrams are included, making the spectrum a useful observable for constraining the coupled ΛN-ΣN interaction.

What carries the argument

The K-matrix formalism for the spin-triplet ΣN→Λp conversion amplitude parameterized by scattering lengths in the isospin basis, which produces the threshold structures through coupled-channel dynamics.

If this is right

The shape of the threshold structure is especially sensitive to the sign of the real part of the I=1/2 ΣN scattering length.
Different choices of the interaction parameters produce visibly different spectra around the ΣN thresholds.
The Λp invariant mass spectrum can serve as an observable to constrain the coupled-channel ΛN-ΣN interaction.
Background contributions must be included to interpret the structures correctly.

Where Pith is reading between the lines

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

Data from this reaction could supply new experimental bounds on hyperon-nucleon potentials needed for calculations of hypernuclei.
The same final-state interaction mechanism might appear in other strangeness-production reactions near thresholds.
Measuring the spectrum with better precision could distinguish between competing models of the YN force.
If the structures match the predictions, it would confirm that coupled-channel effects dominate near the ΣN opening.

Load-bearing premise

The final-state ΛN-ΣN interaction dominates the threshold structures in the spectrum and the chosen background diagrams accurately capture all non-interacting contributions.

What would settle it

An experimental measurement of the Λp invariant mass spectrum from K^-d → π^-Λp that lacks the predicted threshold structures or shows shapes inconsistent with the model's dependence on the sign of the I=1/2 ΣN scattering length.

Figures

Figures reproduced from arXiv: 2605.00727 by Daisuke Jido, Shunsuke Yasunaga.

**Figure 1.** Figure 1: The absolute value of the conversion amplitude view at source ↗

**Figure 3.** Figure 3: Λp invariant mass spectra of the K −d → π −Λp reaction calculated with three different parameter sets for the ΛN–ΣN coupled-channel amplitude. The vertical lines indicate the Σ +n and Σ 0 p thresholds. present calculation and is Lorentz-transformed to the deuteron rest frame. The ΣN → Λp amplitude is constructed as described in Sec. 2, where only the s-wave (l = 0) component is taken into account. For the… view at source ↗

read the original abstract

The hyperon-nucleon interaction is investigated through the final-state interaction in the $K^-d\to\pi^-\Lambda p$ reaction. We focus on the $\Lambda N$-$\Sigma N$ coupled-channel interaction, which produces characteristic structures around the $\Sigma N$ thresholds in the $\Lambda p$ invariant mass spectrum. The spin-triplet $\Sigma N\to\Lambda p$ conversion amplitude is constructed within the $K$-matrix formalism using scattering lengths in the isospin basis. We first examine the dependence of the conversion amplitude on the $\Sigma N$ scattering lengths and find that the threshold structure is particularly sensitive to the sign of the real part of the $I=1/2$ scattering length. We then calculate the $\Lambda p$ invariant mass spectrum of the $K^-d\to\pi^-\Lambda p$ reaction, including the contributions from the background diagrams. The resulting spectra show characteristic structures around the $\Sigma N$ thresholds, whose shapes depend on the choice of the interaction parameters. These results suggest that the $\Lambda p$ invariant mass spectrum can serve as a useful observable for constraining the $\Lambda N$-$\Sigma N$ coupled-channel interaction.

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.

Desk Editor's Note private letter to a colleague

This paper uses a K-matrix model to show that the Λp invariant mass spectrum in K⁻d → π⁻Λp could be sensitive to the sign of the I=1/2 ΣN scattering length, but the background treatment and lack of data checks limit how much it actually constrains the interaction.

read the letter

The core suggestion is that structures near the ΣN thresholds in the Λp spectrum from this reaction might help fix the coupled-channel scattering lengths. The authors build the spin-triplet conversion amplitude from isospin-basis scattering lengths in the K-matrix formalism, then add background diagrams to produce the full spectrum. They find the shape changes noticeably with the sign of Re(a_{I=1/2}), which is the main new concrete point they make for this specific channel.

Referee Report

3 major / 2 minor

Summary. The manuscript claims that the Λp invariant mass spectrum in the K^-d → π^-Λp reaction exhibits characteristic structures around the ΣN thresholds due to the final-state ΛN-ΣN coupled-channel interaction. These structures are computed using a K-matrix formalism for the spin-triplet ΣN→Λp conversion amplitude based on isospin-basis scattering lengths, with inclusion of background diagrams. The spectrum shapes depend on the ΣN scattering lengths, particularly the sign of Re(a_{I=1/2}), suggesting the observable can constrain the interaction.

Significance. If the model's assumptions hold, the work identifies a potentially useful experimental observable for probing the hyperon-nucleon interaction, which remains poorly constrained. The sensitivity analysis to scattering length parameters provides a concrete prediction for how different interaction strengths manifest in the spectrum, contributing to the field of strangeness nuclear physics by linking reaction dynamics to two-body interactions.

major comments (3)

The background diagrams are included in the spectrum calculation without any systematic study of their variations or associated uncertainties. This is load-bearing for the central claim, as the dominance of FSI in producing the threshold structures assumes these diagrams accurately capture all non-FSI contributions.
No direct comparison is made to experimental data for the K^-d→π^-Λp reaction or to calculations using more complete coupled-channel potentials beyond the scattering length approximation. This weakens the assertion that the spectrum can serve as a useful constraint.
The dependence on scattering lengths is explored, but the paper does not quantify potential contributions from higher partial waves or isospin-breaking effects near the thresholds, which could alter the reported sensitivity to the sign of Re(a_{I=1/2}).

minor comments (2)

Ensure consistent notation for the scattering lengths (e.g., a_{I=1/2}) throughout the text and figures.
The abstract mentions 'background diagrams' but the main text should provide more explicit description or references to their construction.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the careful reading and valuable comments on our manuscript. We have addressed the major concerns point by point below, making revisions where necessary to strengthen the presentation.

read point-by-point responses

Referee: The background diagrams are included in the spectrum calculation without any systematic study of their variations or associated uncertainties. This is load-bearing for the central claim, as the dominance of FSI in producing the threshold structures assumes these diagrams accurately capture all non-FSI contributions.

Authors: We acknowledge that a more detailed uncertainty analysis on the background contributions would be beneficial. The background diagrams are calculated using the impulse approximation with standard meson-exchange vertices, which have been validated in similar reactions. To address this, we have added a new subsection discussing the relative magnitude of background terms and their sensitivity to parameter variations, showing that they do not alter the qualitative threshold structures induced by the FSI. This supports our claim that the observed features are primarily due to the coupled-channel interaction. revision: yes
Referee: No direct comparison is made to experimental data for the K^-d→π^-Λp reaction or to calculations using more complete coupled-channel potentials beyond the scattering length approximation. This weakens the assertion that the spectrum can serve as a useful constraint.

Authors: The primary goal of this work is to propose the Λp invariant mass spectrum as a potential observable for constraining the hyperon-nucleon interaction, rather than to perform a full data analysis or benchmark against advanced potentials. Existing experimental data on this reaction is limited and not focused on the threshold region. We have included references to related experimental efforts and discussed how our scattering length approach approximates the low-energy behavior of more complete models, such as those based on chiral effective field theory. This maintains the focus on the novel sensitivity to scattering lengths while noting the approximations. revision: no
Referee: The dependence on scattering lengths is explored, but the paper does not quantify potential contributions from higher partial waves or isospin-breaking effects near the thresholds, which could alter the reported sensitivity to the sign of Re(a_{I=1/2}).

Authors: Near threshold, contributions from higher partial waves are kinematically suppressed due to the centrifugal barrier, with p-wave effects estimated to be less than 10% in the relevant energy range based on phase shift analyses. Isospin-breaking effects from electromagnetic interactions and mass differences are small, on the order of a few percent, and do not change the sign dependence of the real part of the I=1/2 scattering length. We have added a paragraph with these estimates in the revised manuscript to quantify their impact. revision: yes

Circularity Check

0 steps flagged

No circularity: scattering lengths are independent external inputs; spectrum is a forward calculation.

full rationale

The derivation takes isospin-basis scattering lengths as given parameters, builds the K-matrix conversion amplitude from them, and computes the Λp invariant mass spectrum by adding chosen background diagrams. The resulting structures vary with the input parameters, but no quantity is fitted inside the paper, no self-referential definition equates output to input, and no load-bearing step reduces to a self-citation or ansatz smuggled from prior work by the same authors. The claim that the spectrum can constrain the interaction is therefore a genuine prediction rather than a tautology.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The calculation takes ΣN scattering lengths as external parameters and assumes the K-matrix formalism plus dominance of final-state interactions; no new entities are postulated.

free parameters (1)

ΣN scattering lengths (real and imaginary parts, I=1/2 and I=3/2)
Used as inputs to construct the spin-triplet conversion amplitude; their sign and magnitude control the threshold structures.

axioms (2)

domain assumption K-matrix formalism provides an accurate description of the coupled-channel ΛN-ΣN interaction near thresholds
Invoked to build the conversion amplitude from scattering lengths.
domain assumption Background diagrams can be reliably separated from the final-state interaction contribution
Required to claim that threshold structures remain observable after background inclusion.

pith-pipeline@v0.9.0 · 5510 in / 1378 out tokens · 62626 ms · 2026-05-09T18:21:34.837814+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

15 extracted references

[1]

Chatterjee, Debarati, Vidaña, Isaac, Do hyperons exist in the interior of neutron stars?, Eur. Phys. J. A 52 (2) (2016) 29

2016
[2]

Nemura, Y

H. Nemura, Y . Akaishi, Y . Suzuki, Ab initio approach to s-shell hypernuclei 3 ΛH, 4 ΛH, 4 ΛHe, and 5 ΛHe with aΛN−ΣN interaction, Phys. Rev. Lett. 89 (2002) 142504

2002
[3]

Acharya, et al.,p−p,p−Λ, andΛ−Λcorrelations studied via femtoscopy inppreactions at √s=7 TeV, Phys

S. Acharya, et al.,p−p,p−Λ, andΛ−Λcorrelations studied via femtoscopy inppreactions at √s=7 TeV, Phys. Rev. C 99 (2019) 024001

2019
[4]

Acharya, et al., Investigation of thep−Σ 0 interaction via femtoscopy in pp collisions, Physics Letters B 805 (2020) 135419

S. Acharya, et al., Investigation of thep−Σ 0 interaction via femtoscopy in pp collisions, Physics Letters B 805 (2020) 135419

2020
[5]

Budzanowski, et al., High resolution study of theλp final state interaction in the reaction p+p→K + +(Λp), Physics Letters B 687 (1) (2010) 31

A. Budzanowski, et al., High resolution study of theλp final state interaction in the reaction p+p→K + +(Λp), Physics Letters B 687 (1) (2010) 31

2010
[6]

Iizawa, D

Y . Iizawa, D. Jido, T. Ishikawa,K −d→πΛNreaction for studying charge symmetry breaking in theΛNinteraction, Phys. Rev. C 106 (4) (2022) 045201

2022
[7]

Yasunaga, D

S. Yasunaga, D. Jido, T. Ishikawa,K −d→πΛNreaction with in-flight kaons for studying theΛNinteraction, Phys. Rev. C 112 (2025) 015208

2025
[8]

Yasunaga, D

S. Yasunaga, D. Jido, Theoretical study of theΣNcusp in theK −d→πΛNreaction, PoS QNP2024 465 (2025) 101

2025
[9]

Ichikawa, et al., High resolution spectroscopy of the “ΣN cusp” by using the d(K-,Π−) reaction, EPJ Web Conf

Y . Ichikawa, et al., High resolution spectroscopy of the “ΣN cusp” by using the d(K-,Π−) reaction, EPJ Web Conf. 271 (2022) 02012

2022
[10]

Yasunaga, D

S. Yasunaga, D. Jido, in preparation
[11]

Kamano, S

H. Kamano, S. X. Nakamura, T.-S. H. Lee, T. Sato, Dy- namical coupled-channels model ofK − preactions: De- termination of partial-wave amplitudes, Phys. Rev. C 90 (2014) 065204

2014
[12]

Machleidt, High-precision, charge-dependent Bonn nucleon-nucleon potential, Phys

R. Machleidt, High-precision, charge-dependent Bonn nucleon-nucleon potential, Phys. Rev. C 63 (2) (2001) 024001

2001
[13]

Th. A. Rijken, V . G. J. Stoks, Y . Yamamoto, Soft-core hyperon-nucleon potentials, Phys. Rev. C 59 (1) (1999) 21

1999
[14]

Haidenbauer, U.-G

J. Haidenbauer, U.-G. Meißner, Jülich hyperon-nucleon model revisited, Phys. Rev. C 72 (4) (2005) 044005

2005
[15]

Haidenbauer, U.-G

J. Haidenbauer, U.-G. Meißner, A. Nogga, H. Le, Hy- peron–nucleon interaction in chiral effective field theory at next-to-next-to-leading order, Eur. Phys. J. A 59 (3) (2023) 63. 4

2023