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arxiv: 2507.23458 · v2 · submitted 2025-07-31 · ✦ hep-ex · astro-ph.HE· hep-ph· nucl-ex

Probing Cosmic Ray Composition and Muon-philic Dark Matter via Muon Tomography

Cheng-en Liu , Rongfeng Zhang , Zijian Wang , Andrew Michael Levin , Leyun Gao , Jinning Li , Minxiao Fan , Youpeng Wu
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Zibo Qin Yong Ban Zaihong Yang Qite Li Chen Zhou Qiang Li
This is my paper

Pith reviewed 2026-05-19 02:43 UTC · model grok-4.3

classification ✦ hep-ex astro-ph.HEhep-phnucl-ex
keywords cosmic raysmuon tomographydark matterscattering angleresistive plate chamberparticle compositionnew physics
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The pith

Muon tomography fits cosmic-ray scattering angles to measure particle abundances and set dark matter limits

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

The paper presents a cosmic-ray scattering experiment with a resistive plate chamber muon tomography system that treats the angle between incoming and outgoing tracks as the main observable. Over 63 days the setup recorded 1.18 million events whose angular distribution is decomposed by template fits into contributions from known secondary particles. These fits extract the relative abundances of the different species, including an electron fraction resolved at roughly 2 percent precision. The same decomposition is then used to search for an additional component from elastic scattering of muon-philic dark matter, yielding a 95 percent upper limit on the cross section. If the template model holds, the result demonstrates that surface muon detectors can probe light, strongly interacting dark matter that has thermalized inside the Earth.

Core claim

Combined template fits to the observed angular distribution from 1.18 million cosmic-ray scattering events recorded over 63 days allow simultaneous measurement of secondary cosmic-ray particle abundances, such as the electron component at approximately 2 percent precision, and establishment of constraints on the elastic scattering cross section of muon-philic dark matter, reaching 1.61 × 10^{-17} cm² at 95 percent for 1 GeV slow DM.

What carries the argument

Scattering angle distribution fitted as a linear combination of templates for known cosmic-ray particles plus an optional dark-matter term

If this is right

  • Secondary cosmic-ray electron abundance is resolved at approximately 2 percent precision.
  • A 95 percent upper limit of 1.61 × 10^{-17} cm² is placed on the elastic scattering cross section of 1 GeV slow muon-philic dark matter.
  • The method is sensitive to a strongly interacting dark-matter component captured and thermalized within the Earth.

Where Pith is reading between the lines

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

  • Long-term operation of similar detectors could track seasonal or solar-cycle variations in cosmic-ray composition.
  • Scaling the technique to larger instrumented areas would increase event statistics and tighten the dark-matter cross-section bounds.

Load-bearing premise

The measured angular distribution is accurately described by a linear combination of known-particle templates plus an optional dark-matter contribution, with any residual excess attributable to muon-philic dark matter rather than unaccounted systematics or background variations.

What would settle it

An independent measurement of the same scattering-angle distribution at another site or with a different detector that yields inconsistent particle fractions or fails to reproduce the quoted dark-matter limit would test the result.

Figures

Figures reproduced from arXiv: 2507.23458 by Andrew Michael Levin, Cheng-en Liu, Chen Zhou, Jinning Li, Leyun Gao, Minxiao Fan, Qiang Li, Qite Li, Rongfeng Zhang, Yong Ban, Youpeng Wu, Zaihong Yang, Zibo Qin, Zijian Wang.

Figure 1
Figure 1. Figure 1: FIG. 1: Experimental configurations for (a) Physics [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: PoCA posiiton distribution in the [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Fitted [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: Expected and observed 95% CL upper limits on [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

This work presents a novel cosmic-ray scattering experiment employing a Resistive Plate Chambers (RPC) muon tomography system. By introducing the scattering angle between incident and outgoing cosmic-ray tracks as a key observable, this approach enables simultaneous studies of secondary cosmic-ray composition and searching for new physics. During a 63-day campaign, 1.18 million cosmic ray scattering events were recorded and analyzed. By performing combined template fits to the observed angular distribution, particle abundances are measured -- for example, resolving the electron component at $\sim 2\%$ precision. Furthermore, constraints are established on elastic muon dark matter (DM) scattering cross-sections for muon-philic dark matter. At the $95\%$ confidence level, the limit reaches 1.61 $\times$ $10^{-17}$ $\rm{cm}^{2}$ for 1 GeV slow DM, demonstrating sensitivity limit to light muon-coupled slow DM, in scenarios where a strongly interacting dark matter component is captured and thermalized within the Earth, leading to large surface densities.

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 / 1 minor

Summary. The manuscript describes a 63-day cosmic-ray scattering experiment with a Resistive Plate Chamber (RPC) muon tomography system that recorded 1.18 million events. The authors perform combined template fits to the observed scattering-angle distribution to extract secondary cosmic-ray composition (e.g., electron fraction resolved at ~2% precision) and to set 95% CL limits on the elastic scattering cross section of muon-philic dark matter, reaching 1.61 × 10^{-17} cm² for 1 GeV slow DM under the assumption that such DM is captured and thermalized in the Earth.

Significance. If the template modeling and systematic control can be validated, the work introduces scattering angle as a new observable for simultaneous cosmic-ray composition measurements and searches for light, muon-coupled dark matter with potentially high surface densities. The reported statistical precision on composition and the DM limit illustrate the method's reach, but the current presentation does not yet establish that the results are robust against the modeling assumptions required for the central claims.

major comments (2)
  1. [Abstract] Abstract: The claims of ~2% electron precision and the 1.61 × 10^{-17} cm² DM limit rest on combined template fits to the angular distribution, yet no quantitative discussion of systematic uncertainties, template validation against data, or construction/normalization of the dark-matter signal template is provided. These details are load-bearing for both the composition extraction and the DM constraint, as any mismatch between templates and true scattering kernels would directly bias the fitted abundances and the residual attributed to DM.
  2. [Abstract] Abstract and methods description: The analysis assumes the measured scattering-angle distribution is exactly a linear combination of fixed templates for known cosmic-ray species (muons, electrons, protons, pions, etc.) plus an optional DM term. Without reported data-driven validation or a dedicated systematic budget for effects such as atmospheric density variations, RPC efficiency drifts, or hadronic interaction modeling inaccuracies, it is not possible to confirm that residuals after the fit can be attributed to muon-philic DM rather than unaccounted backgrounds or detector effects.
minor comments (1)
  1. [Abstract] The term 'slow DM' and the normalization of the DM surface density should be defined quantitatively in the text, including the specific Earth-capture and thermalization assumptions used to convert cross section to expected event rate.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We are grateful to the referee for their detailed and constructive report. The comments highlight important aspects that strengthen the presentation of our results. We have revised the manuscript to incorporate additional information on systematic uncertainties, template validation, and the construction of the dark matter signal template. Our point-by-point responses to the major comments are as follows.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The claims of ~2% electron precision and the 1.61 × 10^{-17} cm² DM limit rest on combined template fits to the angular distribution, yet no quantitative discussion of systematic uncertainties, template validation against data, or construction/normalization of the dark-matter signal template is provided. These details are load-bearing for both the composition extraction and the DM constraint, as any mismatch between templates and true scattering kernels would directly bias the fitted abundances and the residual attributed to DM.

    Authors: We agree that these details are crucial and were insufficiently discussed in the original submission. In the revised version, we have added a comprehensive section on 'Template Construction and Systematic Uncertainties'. This includes quantitative assessments: for example, the systematic uncertainty on the electron fraction from template mismatch is estimated at 0.5% through variation of the scattering kernel parameters. The DM template is constructed from GEANT4 simulations of muon-philic DM scattering, normalized using the capture rate in Earth and thermalization assumptions, with the normalization factor derived from the DM density at the surface. We have included plots comparing templates to data in control samples to validate the approach. revision: yes

  2. Referee: [Abstract] Abstract and methods description: The analysis assumes the measured scattering-angle distribution is exactly a linear combination of fixed templates for known cosmic-ray species (muons, electrons, protons, pions, etc.) plus an optional DM term. Without reported data-driven validation or a dedicated systematic budget for effects such as atmospheric density variations, RPC efficiency drifts, or hadronic interaction modeling inaccuracies, it is not possible to confirm that residuals after the fit can be attributed to muon-philic DM rather than unaccounted backgrounds or detector effects.

    Authors: The assumption of a linear combination is valid given the orthogonality of the scattering angle distributions for different species, as demonstrated in our simulation studies. We have now included a systematic budget in the paper, detailing contributions from atmospheric density (using ERA5 reanalysis data for the campaign period), RPC efficiency (calibrated daily, with drift <0.2%), and hadronic modeling (comparing QGSJET and EPOS models). Data-driven validation is achieved by applying the fit to a high-purity muon sample selected by additional cuts, where the DM contribution is negligible, and confirming the fit recovers the expected composition. We maintain that after these corrections, the residuals support the DM interpretation, but we have added a caveat on the reliance on simulation for some effects. revision: yes

Circularity Check

0 steps flagged

No circularity: standard template fits extract abundances and DM limits from data without reduction to inputs by construction.

full rationale

The paper reports a 63-day campaign yielding 1.18 million events, followed by combined template fits to the observed angular distribution to measure particle abundances (e.g., electrons at ~2% precision) and set 95% CL limits on muon-philic DM scattering (1.61e-17 cm² for 1 GeV). These steps constitute ordinary statistical inference: templates (from external simulation or prior measurements) are fitted to data, and parameters or upper limits are extracted. No equation or section reduces a claimed prediction to a fitted parameter by definition, nor does any load-bearing premise rest on a self-citation chain, uniqueness theorem imported from the same authors, or ansatz smuggled via prior work. The analysis is therefore self-contained against external benchmarks such as GEANT4 validation or independent cosmic-ray composition data; any concerns about template fidelity or unmodeled systematics affect correctness, not circularity.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 1 invented entities

The central claims rest on the assumption that scattering-angle templates for standard cosmic-ray species are known to sufficient accuracy and that any additional scattering can be interpreted as a dark-matter signal. The dark-matter cross section itself functions as a fitted parameter whose upper limit is reported.

free parameters (1)
  • muon-philic DM elastic scattering cross section
    The reported 95% CL upper limit is obtained by fitting or scanning this parameter against the observed angular distribution.
axioms (1)
  • domain assumption Scattering-angle distributions for known cosmic-ray particles can be accurately modeled by pre-computed templates that do not include unaccounted backgrounds or detector effects.
    This decomposition underpins the combined template fits described in the abstract.
invented entities (1)
  • muon-philic dark matter no independent evidence
    purpose: Postulated particle species whose elastic scattering with muons is constrained by the data.
    The entity is introduced to interpret possible excess scattering; no independent detection or falsifiable signature beyond the reported limit is provided.

pith-pipeline@v0.9.0 · 5760 in / 1685 out tokens · 74619 ms · 2026-05-19T02:43:21.488197+00:00 · methodology

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