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Effects of femtoscopic correlations on spin-spin correlation measurements

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Bijun Fan, Like Liu, Shusu Shi

Nuclear Theory · Submitted 24 Aug 2026 · 39 references

Pith's reading: Spin-dependent femtoscopic correlations can create a fake spin-spin correlation signal for Lambda pairs at low relative momentum, with magnitude comparable to preliminary CMS values.

T0 · AI review

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arXiv ID2608.22707 (version 1)
Pith IDHRCKQUJS, Pith's permanent record of this paper and its review
CitationBijun Fan, Like Liu, Shusu Shi. "Effects of femtoscopic correlations on spin-spin correlation measurements." arXiv:2608.22707 (2026). https://pith.science/paper/HRCKQUJS
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Claim paper
The paper

The paper claims

Spin-dependent femtoscopic correlations can create a fake spin-spin correlation signal for Lambda pairs at low relative momentum, with magnitude comparable to preliminary CMS values.

The reading

Lambda particles produced in high-energy collisions reveal their spin through the direction of the proton they emit when they decay. To measure whether two Lambdas have aligned spins, physicists look at the opening angle between the two decay protons, cosθ*. This paper asks whether a known quantum effect, femtoscopic correlations from quantum statistics and final-state interactions, can distort the measured cosθ* distribution.

The authors use the AMPT event generator to create Lambda pairs with no intrinsic spin correlation. Each pair is then weighted by a correlation function that depends on its relative momentum and on whether the pair is in a spin-singlet or spin-triplet state. Because the probability that a pair with a given cosθ* is singlet or triplet changes with cosθ*, the weighting tilts the angle distribution. The result is a slope in cosθ* where none existed, which is indistinguishable from a real spin correlation.

The tilt is largest for pairs with relative momentum q_inv below 0.2 GeV/c. In that region the predicted fake signal is comparable in size to the preliminary CMS measurement. When the full q_inv range is used, the bias mostly averages away. The authors do not claim the current CMS result is wrong; they provide a framework for estimating the bias in future differential analyses that emphasize low relative momentum.

Extended reading notes

Core claim

Spin-dependent femtoscopic correlations generate a fake spin-spin correlation signal in the cosθ* distribution of Lambda pairs, and in the low-q_inv region this bias is comparable in magnitude to the preliminary CMS spin-correlation signal. The abstract states: "femtoscopic weighting induces an apparent angular modulation, creating a fake correlation signal even when no intrinsic spin correlation is present" and "the combined femtoscopic effect reaches a magnitude comparable to that of the preliminary CMS measurements" in the low-q_inv region.

Load-bearing premise

The quantitative magnitude of the predicted bias depends on the source radii and the spin-channel-separated scattering lengths in Table I. The paper states these are motivated by previous measurements but that the available data do not precisely determine the interaction parameters separately for the spin-singlet and spin-triplet channels. If the true singlet-triplet difference in the correlation functions is much smaller or larger than assumed, the claimed 'comparable to CMS' magnitude would change correspondingly.

Original abstract

Hyperon spin correlations serve as sensitive probes of spin dynamics in high-energy collisions, yet their extraction from weak-decay angular distributions can be contaminated by femtoscopic effects due to quantum statistics and final-state interactions. In this work, we quantitatively assess this contamination for $\Lambda\Lambda$ and $\Lambda\bar{\Lambda}$ pairs using the AMPT model combined with spin-dependent weights from the Lednick\'y--Lyuboshits formalism. Because the singlet and triplet spin configurations contribute differently to the decay-angle distribution, femtoscopic weighting induces an apparent angular modulation, creating a fake correlation signal even when no intrinsic spin correlation is present. We find that the induced bias can become substantial in the low-$q_{\mathrm{inv}}$ region, where the combined femtoscopic effect reaches a magnitude comparable to that of the preliminary CMS measurements. Our results establish a framework for evaluating such systematics, highlighting that femtoscopic corrections must be carefully considered in future differential analyses that emphasize the low-relative-momentum region.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,458 input tokens.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.47 · human participants 0.01 · controlled comparison 0.13 · randomized assignment 0.01 · states quantitative result 0.23 · compares with prior results 0.90 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

Hyperon spin correlations serve as sensitive probes of spin dynamics in high-energy collisions, yet their extraction from weak-decay angular distributions can be contaminated by femtoscopic effects due to quantum statistics and final-state interactions. In this work, we quantitatively assess this contamination for $\Lambda\Lambda$ and $\Lambda\bar{\Lambda}$ pairs using the AMPT model combined with spin-dependent weights from the Lednick\'y--Lyuboshits formalism. Because the singlet and triplet spin configurations contribute differently to the decay-angle distribution, femtoscopic weighting induces an apparent angular modulation, creating a fake correlation signal even when no intrinsic spin correlation is present. We find that the induced bias can become substantial in the low-$q_{\mathrm{inv}}$ region, where the combined femtoscopic effect reaches a magnitude comparable to that of the preliminary CMS measurements. Our results establish a framework for evaluating such systematics, highlighting that femtoscopic corrections must be carefully considered in future differential analyses that emphasize the low-relative-momentum region.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 Hyperon spin correlations serve as sensitive probes of spin dynamics in high-energy collisions, yet their extraction from weak-decay angular distributions can be contaminated by femtoscopic effects due to quantum statistics and final-state interactions. background 0.99 0.05 0.04 asserted 0.73
s1 In this work, we quantitatively assess this contamination for $\Lambda\Lambda$ and $\Lambda\bar{\Lambda}$ pairs using the AMPT model combined with spin-dependent weights from the Lednick\'y--Lyuboshits formalism. method 0.70 0.94 0.04 asserted 0.98
s2 Because the singlet and triplet spin configurations contribute differently to the decay-angle distribution, femtoscopic weighting induces an apparent angular modulation, creating a fake correlation signal even when no intrinsic spin correlation is present. interpretation 0.61 0.39 0.29 asserted 1.00
s3 We find that the induced bias can become substantial in the low-$q_{\mathrm{inv}}$ region, where the combined femtoscopic effect reaches a magnitude comparable to that of the preliminary CMS measurements. result 1.00 0.96 0.53 asserted 0.92
s4 Our results establish a framework for evaluating such systematics, highlighting that femtoscopic corrections must be carefully considered in future differential analyses that emphasize the low-relative-momentum region. future work 0.71 0.74 0.62 asserted 0.97

What kind of paper the classifier reports this is: simulation study 1.00 · evidence from simulation or computation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1. Spin-state weights for the spin-singlet (
Figure 2. FIG. 2. Distributions of the correlation function
Figure 3. This differential representation allows the depen
Figure 4. FIG. 4. Comparison of the fitted and injected ΛΛ spin-correlation strengths in
Figure 5. FIG. 5. Comparison of the extracted spin-correlation strengths as a function of ∆

Figures reproduced from arXiv:2608.22707 by the authors.

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References
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What this paper does with the arXiv papers it cites

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

What it cites · 11 sentences without a confident label

Uses the method or tool of 6 papers
Cites as background 4 papers
  • Despite their long-standing role as a sensitive probe of particle-emission sources and low-energy two-particle interactions, femtoscopic correlations arising from quantum statistics and final-state interactions [ref] have been largely overlooked in the context of spin-spin correlation measurements.

    Correlation femtoscopy of multiparticle processes · Introduction · 0.88

  • In the strange-baryon sector, the BESIII Collaboration has tested local realism using entangled $ΛΛ̅$ pairs produced in $e^+e^-$ collisions [ref] , while STAR and CMS have reported spin-spin correlations for $ΛΛ̅$, $ΛΛ$, and $Λ̅Λ̅$ pairs in high-energy $p$+$p$ collisions [ref] .

    2506.05499 · Introduction · 0.86

  • In the strange-baryon sector, the BESIII Collaboration has tested local realism using entangled $ΛΛ̅$ pairs produced in $e^+e^-$ collisions [ref] , while STAR and CMS have reported spin-spin correlations for $ΛΛ̅$, $ΛΛ$, and $Λ̅Λ̅$ pairs in high-energy $p$+$p$ collisions [ref] .

    2505.14988 · Introduction · 0.86

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