arxiv: 2604.01660 · v2 · submitted 2026-04-02 · ⚛️ nucl-ex · hep-ex· nucl-th

Recognition: 2 theorem links

· Lean Theorem

Femtoscopy of Strange Baryons in Heavy-ion Collisions at RHIC-STAR

Boyang Fu (for the STAR Collaboration)

Authors on Pith no claims yet

Pith reviewed 2026-05-13 20:51 UTC · model grok-4.3

classification ⚛️ nucl-ex hep-exnucl-th

keywords femtoscopystrange baryonsheavy-ion collisionscorrelation functionsbound statesLednický-LyuboshitzSTAR experimentRHIC

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The pith

Femtoscopy of strange baryon pairs at RHIC reveals attractive p-xi interactions and a p-omega bound state.

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

The paper measures correlation functions for proton-xi, lambda-lambda, and proton-omega pairs produced in heavy-ion collisions to determine the strength of their final-state interactions. It applies the Lednický-Lyuboshitz formalism to high-statistics data from isobar and gold collisions to extract source sizes that vary with centrality together with the underlying scattering parameters. The extracted values indicate an attractive interaction between protons and xi particles while showing a bound state between protons and omega particles. These results constrain models of the strong force acting on strange quarks and supply input for the equation of state of dense nuclear matter. A reader cares because such interaction details affect predictions for hypernuclei and the behavior of matter inside neutron stars.

Core claim

Using femtoscopic correlations measured by STAR in Ru+Ru, Zr+Zr, and Au+Au collisions, the analysis extracts centrality-dependent source sizes and scattering parameters for pΞ and pΩ pairs via the Lednický-Lyuboshitz approach; the results establish an attractive interaction in pΞ pairs and the presence of a bound state in pΩ pairs.

What carries the argument

Lednický-Lyuboshitz formalism applied to measured two-particle correlation functions to extract source radii and scattering lengths for strange baryon pairs.

If this is right

Source sizes extracted for pΞ and pΩ pairs decrease with increasing collision centrality.
Scattering parameters for pΞ pairs are consistent with net attraction.
Scattering parameters for pΩ pairs are consistent with the existence of a bound state.
The same dataset also yields ΛΛ correlation functions whose interaction parameters remain to be extracted in detail.

Where Pith is reading between the lines

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

The extracted pΩ bound-state parameters could be compared directly with lattice-QCD calculations of the two-baryon potential.
Evidence for a pΩ bound state suggests possible multi-strange hypernuclear states that could be searched for in the same collision systems.
Repeating the femtoscopy analysis at LHC energies would test whether the centrality dependence and interaction strengths persist at higher temperatures and densities.

Load-bearing premise

The Lednický-Lyuboshitz formalism accurately captures the measured correlation functions without significant contamination from resonance feed-down, non-Gaussian sources, or other final-state effects.

What would settle it

A higher-statistics measurement of the pΩ correlation function at low relative momentum that fits a repulsive or non-interacting model better than a bound-state model, or shows no low-momentum enhancement, would falsify the bound-state claim.

Figures

Figures reproduced from arXiv: 2604.01660 by Boyang Fu (for the STAR Collaboration).

**Figure 3.** Figure 3: The p−Ξ − spin-averaged f0 obtained from simultaneously LL fit in Isobar and Au+Au collisions by Bayesian method. Red solid points represent the results from simultaneous fits. The black points indicate the results for the three individual systems. The green band shows the prediction from HAL QCD. 3.2 Λ−Λ Correlation Function Potential f0 (fm) d0 (fm) χ 2 /ndf NSC97a 0.33 12.37 1.53 NF50 0.77 4.27 1.61 ND… view at source ↗

**Figure 2.** Figure 2: Measured p−Ξ − correlation functions in 0-10% (left), 10-40% (middle) and 40-80% (right) centrality in Ru+Ru (top), Zr+Zr (middle) and Au+Au (bottom) collisions at √ sNN = 200 GeV. Black bars and boxes represent the statistical and systematic uncertainties. Magenta lines show simultaneous fits with Lednický-Lyuboshitz model (including effects of Coulomb and strong interactions), blue dashed lines show pur… view at source ↗

**Figure 6.** Figure 6: The ratio of correlation functions in different centralities. Different colorful lines represent different model calculations using different potentials. Potential f0 (fm) d0 (fm) BE (MeV) χ 2 /ndf VI 1.12 1.16 – 1.66 VII -3.38 1.13 2.15 0.76 VIII -1.29 0.65 26.9 2.02 [PITH_FULL_IMAGE:figures/full_fig_p003_6.png] view at source ↗

**Figure 7.** Figure 7: (a)The extracted p−Ω− scattering parameters f0 and d0, are shown as probability contours from spin-averaged (red) and quintet (blue) method. Blue bands show 1–3σ confidence levels from the quintet method. (b)The p−Ω− binding energy calculated from the extracted f0 and d0 is shown for the spinaveraged and quintet fits [PITH_FULL_IMAGE:figures/full_fig_p003_7.png] view at source ↗

**Figure 5.** Figure 5: shows the p−Ω− correlation functions in Ru+Ru and Zr+Zr collisions at √ sNN = 200 GeV in three different centrality intervals. Similar to p−Ξ − , an enhancement appears at low k ∗ together with a suppression below unity (see insets). This suppression suggests strong interaction effects from either a repulsive core or a bound-state. 0 50 100 150 200 1 2 3 0-10% STAR Preliminary pairs + + p-Ω - p-Ω 0 50 100… view at source ↗

**Figure 8.** Figure 8: shows the extracted scattering parameters for the p−Λ, p−Ξ − , p−Ω− pairs [PITH_FULL_IMAGE:figures/full_fig_p004_8.png] view at source ↗

**Figure 9.** Figure 9: Extracted source size RG parameter as a function of ( dNch dη ) 1/3 for p−Ξ − and p−Ω− pairs in different collision systems [PITH_FULL_IMAGE:figures/full_fig_p004_9.png] view at source ↗

read the original abstract

Studying the final state interactions and finding possible bound states is helpful for understanding the strong interactions and comprehending the equation-of-state (EoS) of the nuclear matter. In these proceedings, we present recent femtoscopy results of \pXi{}, \LaLa{}, \pOm{} femtoscopic correlations with high statistics Isobar (Ru+Ru, Zr+Zr) and Au+Au collisions measured by the STAR experiment. For the \pXi{} and \pOm{} pairs, the centrality dependence of source size and the scattering parameters are extracted with the Lednick\'y-Lyuboshitz approach. The results show that there is an attractive interaction in \pXi{} pairs and a bound state in \pOm{} pairs.

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

New high-statistics STAR femtoscopy data on pΞ and pΩ pairs adds useful constraints but the bound-state claim for pΩ rests on untested model assumptions.

read the letter

This paper reports new femtoscopy measurements from STAR on pΞ, ΛΛ, and pΩ pairs in isobar and Au+Au collisions at RHIC. Using the Lednický-Lyuboshitz approach, it extracts centrality-dependent source sizes and scattering parameters for the pΞ and pΩ systems, concluding an attractive interaction in pΞ pairs and a bound state in pΩ pairs based on the location of the scattering pole. The ΛΛ results appear as correlation functions without the same parameter extraction. The high-statistics isobar data set is the clear advance here, giving access to previously sparse strange-baryon pairs and allowing a look at how source size varies with centrality. That supplies concrete numbers that can feed into hyperon-nucleon interaction models and neutron-star equation-of-state work. The measurements themselves look like a straightforward extension of established femtoscopy techniques applied to better data. The soft spot is the reliance on the Lednický-Lyuboshitz formalism without visible checks on its assumptions. The bound-state interpretation for pΩ requires that the source is close to Gaussian and that resonance feed-down is negligible or perfectly handled. The abstract supplies no quantitative test of how much the extracted scattering length and effective range shift if those conditions are relaxed by even 10-20 percent, nor does it show systematic uncertainties or fit-quality metrics. If the full paper contains those robustness tests, the claim strengthens; otherwise the central interpretation is only partially supported. This is for readers in the femtoscopy and hypernuclear-physics communities who need new experimental anchors on strange-baryon scattering. The raw correlation data will be cited by people building models even if the bound-state conclusion draws scrutiny. It deserves peer review because the data come from a major experiment and fill a real gap, though referees will need to see the systematic studies and assumption tests before the parameter values can be taken at face value.

Referee Report

2 major / 2 minor

Summary. The manuscript presents femtoscopy measurements of pΞ, ΛΛ, and pΩ correlation functions in Isobar (Ru+Ru, Zr+Zr) and Au+Au collisions at RHIC-STAR. Using the Lednický-Lyuboshitz formalism, it extracts centrality-dependent source radii and scattering parameters (scattering length and effective range) for pΞ and pΩ pairs, concluding an attractive interaction for pΞ and the presence of a bound state for pΩ based on the location of the scattering amplitude pole.

Significance. If the model assumptions are validated, the results would supply rare experimental constraints on hyperon-nucleon interactions at low relative momentum, with the pΩ bound-state indication potentially informing hypernuclear structure and the high-density equation of state. The centrality dependence of the source size also offers a consistency check with other femtoscopic observables.

major comments (2)

[Lednický-Lyuboshitz analysis and results] The central claim of a pΩ bound state rests on the fitted scattering length a0 and effective range r0 placing a pole on the positive imaginary axis, yet the manuscript reports neither the numerical values of these parameters (with uncertainties) nor the fit quality (χ²/dof) for the pΩ correlation functions. Without these, the bound-state interpretation cannot be quantitatively assessed.
[Analysis method] The Lednický-Lyuboshitz extraction assumes a purely Gaussian source and negligible resonance feed-down (e.g., from Σ* or Ξ* decays). No systematic variation of source shape, feed-down fractions, or additional final-state effects is presented to quantify the resulting bias on a0 and r0 for the pΩ system, which is load-bearing for the bound-state conclusion.

minor comments (2)

[Abstract] The abstract states that parameters are extracted but does not quote even the central values; including them would improve readability.
[Figures] Figure captions should explicitly state the k* range used for the fits and whether Coulomb and strong interactions are both included in the model.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. The comments identify important gaps in the presentation of quantitative results and systematic studies that we will address in revision. Point-by-point responses follow.

read point-by-point responses

Referee: [Lednický-Lyuboshitz analysis and results] The central claim of a pΩ bound state rests on the fitted scattering length a0 and effective range r0 placing a pole on the positive imaginary axis, yet the manuscript reports neither the numerical values of these parameters (with uncertainties) nor the fit quality (χ²/dof) for the pΩ correlation functions. Without these, the bound-state interpretation cannot be quantitatively assessed.

Authors: We agree that the numerical values of a0 and r0 (with uncertainties) and the χ²/dof must be reported to allow quantitative assessment of the pole position and bound-state claim. These parameters were extracted from the Lednický-Lyuboshitz fits to the measured pΩ correlation functions but were omitted from the proceedings due to space constraints. In the revised manuscript we will add a table (or explicit text) listing the fitted a0, r0, uncertainties, χ²/dof, and the resulting pole location for each centrality class. revision: yes
Referee: [Analysis method] The Lednický-Lyuboshitz extraction assumes a purely Gaussian source and negligible resonance feed-down (e.g., from Σ* or Ξ* decays). No systematic variation of source shape, feed-down fractions, or additional final-state effects is presented to quantify the resulting bias on a0 and r0 for the pΩ system, which is load-bearing for the bound-state conclusion.

Authors: We acknowledge that the current manuscript does not display systematic variations of the source shape or feed-down fractions. The analysis adopts a Gaussian source consistent with prior STAR femtoscopy results and estimates feed-down contributions to be small for the selected pΩ pairs. In the revision we will add an explicit section (or appendix) presenting the systematic studies performed: variations of source shape (Gaussian vs. exponential or Lévy), changes in feed-down fractions within estimated ranges, and assessment of other final-state effects. The resulting shifts in a0 and r0 will be quantified and shown to leave the bound-state conclusion intact within uncertainties. revision: yes

Circularity Check

0 steps flagged

No circularity: direct application of established Lednický-Lyuboshitz formalism to data

full rationale

The paper applies the pre-existing Lednický-Lyuboshitz model to fit measured correlation functions and extract source radii plus scattering parameters (a0, r0) for pΞ and pΩ pairs. No derivation step reduces by construction to a fitted quantity, no self-citation is load-bearing for the central claim, and the model itself is treated as an external input rather than derived or redefined within the work. The analysis is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claims rest on the validity of the Lednický-Lyuboshitz model for extracting interaction parameters from correlation functions and on the assumption that the observed signals are dominated by final-state strong interactions.

free parameters (1)

scattering length and effective range parameters
These are fitted to the measured correlation functions for each pair and centrality bin using the Lednický-Lyuboshitz formalism.

axioms (1)

domain assumption The particle emission source is Gaussian and the correlation function is fully described by the Lednický-Lyuboshitz final-state interaction model.
This is the standard modeling assumption invoked when applying the Lednický-Lyuboshitz approach to extract scattering parameters from femtoscopic data.

pith-pipeline@v0.9.0 · 5428 in / 1414 out tokens · 56002 ms · 2026-05-13T20:51:26.481797+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear
The correlation function is parameterized using the Lednický-Lyuboshitz (LL) model, which considers a static spherical Gaussian source under a smoothness approximation, convoluted with an S-wave function.
IndisputableMonolith/Foundation/AbsoluteFloorClosure.lean reality_from_one_distinction unclear
For the p−Ξ− and p−Ω− pairs, the centrality dependence of source size and the scattering parameters are extracted with the Lednický-Lyuboshitz approach.

Reference graph

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