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REVIEW 3 major objections 4 minor 28 references

Atmospheric muon flux suppression at potential new low-radiation underground physics laboratory in Israel

T0 review · 3 major / 4 minor · reviewed 2026-08-16 · deepseek-v4-flash

Pith's one-line read A tunnel under Kokhav HaYarden suppresses atmospheric muons by a factor of 4,456, with an effective overburden of about 873 m.w.e.

desk verdict A useful first muon-flux measurement at a candidate Israeli underground site, with a plausible suppression factor, but the claimed precision rests on an unquantified above-ground dead-time correction. read the letter →

arxiv 2504.15102 v1 pith:5IQNOCYS submitted 2025-04-21 physics.ins-det hep-ex

classification physics.ins-dethep-ex
keywords undergroundlaboratoryatmosphericmuonsmuonfluxsuppressionscintillatorhodoscopecosmicrayslow-backgroundexperimentsKokhavHaYardensuperconductingqubits
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper reports the first direct measurement of the residual atmospheric muon flux at a candidate underground laboratory site inside the Kokhav HaYarden pumped-storage tunnels in Israel. Using a four-plate plastic scintillator hodoscope run both above ground and under 361 m of rock, the authors measure a suppression factor of $4456 \pm 77$ relative to sea level, an absolute integrated flux of $3.75 \times 10^{-6}$ cm$^{-2}$ s$^{-1}$, and an effective flat overburden of roughly 873 m.w.e. If the measurement holds, the site would sit at an intermediate depth between shallow and deep underground laboratories, useful for material screening, low-background testing, low-mass dark matter searches, and radiation-sensitive quantum devices. The paper also reports a low radon level of $28.3 \pm 14.0$ Bq m$^{-3}$ and an angular muon shadow from the mountain topography, both supporting the site's working conditions for future experiments.

What carries the argument

The central object is a portable muon hodoscope: four vertically stacked plastic scintillator plates ($144 \times 60 \times 1.2$ cm$^3$) with photomultiplier tubes at both ends of each plate, triggered by a coincidence on the top two plates and read out by two oscilloscopes. Track angles are reconstructed from the time delay between the two PMTs on each plate, giving a one-dimensional position along the plate and hence a zenith angle. The argument is carried by the ratio of trigger rates at the two sites: because the same detector, threshold, and geometry are used above ground and underground, the efficiency and acceptance factors cancel, so the rate ratio is the flux suppression factor. The measured suppression is then converted to an equivalent vertical depth using the differential muon intensity function $I_\mu(h_0) = 68 \times 10^{-6} e^{-h_0/285} + 2 \times 10^{-6} e^{-h_0/698}$ (with $h_0$ in m.w.e.), and cross-checked against a simulation that propagates a Gaisser-parametrized muon spectrum through a two-dimensional slant-depth map built from elevation data.

What would settle it

Run the same hodoscope above ground while lowering the photomultiplier high voltage in steps and record the trigger rate; if the rate does not scale linearly with the muon rate, then the efficiency is rate-dependent and the sea-level rate used in the suppression factor is biased. A second check is to compare the measured angular muon distribution at Kokhav HaYarden with a full muon transport simulation using the actual rock density; a systematic angular offset would implicate the slant-depth model rather than the flux measurement.

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Extended reading notes

Core claim

The central claim is that the integrated atmospheric muon flux at the Kokhav HaYarden site is suppressed by a factor of $4456 \pm 77$ relative to sea level, corresponding to $3.75 \times 10^{-6}$ cm$^{-2}$ s$^{-1}$ and an equivalent vertical depth of about 873 m.w.e. The authors establish this by measuring the trigger rate of a hodoscope with identical geometry at the above-ground Tel Aviv University site and at the underground site, in two orientations, and taking the ratio so that detector efficiency and acceptance cancel. They further show that the angular distribution of reconstructed muon tracks is biased away from the thickest rock overburden, revealing the muon shadow of the mountain, and that the local radon concentration is low. A simplified simulation that propagates a standard parametrization of the sea-level muon spectrum through the slant-depth map predicts about 860 m.w.e., in good agreement with the measured value. The conclusion is that the tunnel branch offers working conditions suitable for a new low-radiation underground laboratory, with the option of 25% more overburden deeper in the tunnel.

Load-bearing premise

The suppression factor assumes that the above-ground trigger rate of about $3.8 \times 10^1$ s$^{-1}$ at Tel Aviv University is not distorted by dead time or by two muons arriving close together, so that the detector's efficiency and acceptance cancel exactly between the above-ground and underground runs; the paper quotes only statistical errors and does not quantify rate-dependent effects.

Editorial extensions

If this is right

  • At roughly 873 m.w.e., the Kokhav HaYarden site sits between shallow and deep underground laboratories, making it a candidate for material screening, high-voltage component testing, low-mass dark matter searches, and some neutrino experiments.
  • The deeper, currently inaccessible part of the tunnel would add about 25% more vertical rock, which would further reduce the muon flux below the already measured suppression.
  • The low radon activity of $28.3 \pm 14.0$ Bq m$^{-3}$ means radon is not a limiting background for the planned uses, although the high temperature and humidity will require attention.
  • The measured angular muon shadow confirms that the slant-depth map built from elevation data captures the real overburden, validating the simulation-based estimate of about 860 m.w.e.
  • The same portable hodoscope and ratio method can be carried to the deeper Manara pumped-storage site, which could reach roughly 2000 m.w.e. and enter the depth class of established deep laboratories.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Inference: if the rate-ratio cancellation is robust, the same hodoscope could be redeployed at Manara with a longer sea-level control run to test for rate-dependent losses, since a small dead-time correction at the high above-ground rate would shift the quoted suppression factor.
  • Inference: the agreement between the measured 873 m.w.e. and simulated 860 m.w.e. suggests the elevation-derived slant-depth map and a uniform rock density of 2.6 g cm$^{-3}$ are adequate for survey-level planning, but a direct density measurement would tighten the depth estimate.
  • Inference: for superconducting qubit experiments, a factor-of-4,456 reduction in ionizing radiation could meaningfully lower radiation-induced quasiparticle poisoning, provided the site's humidity and temperature are controlled.
  • Inference: the measured flux could be compared against depth-flux curves from other intermediate-depth labs; a systematic offset would point to local rock composition or the sea-level normalization rather than the detector.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 4 minor

Summary. The manuscript reports a first exploratory muon-flux measurement at the proposed Kokhav HaYarden (KY) underground site in Israel, using a four-plate plastic scintillator hodoscope with a two-fold (top-plate) coincidence trigger. Data were taken above ground at Tel Aviv University (TAU) and underground at KY in two orientations, South-North and West-East. The central result is a suppression factor of 4456 ± 77 relative to TAU, corresponding to an integrated muon flux of 3.75 ± 0.06 × 10^-6 cm^-2 s^-1 and an effective vertical overburden of roughly 873 m.w.e. The paper also presents angular distributions that show the mountain's muon shadow, a simulation-based slant-depth map, and ancillary radon, temperature, and humidity measurements. The authors state that the quoted uncertainty is statistical only and that constant-efficiency systematics cancel in the ratio.

Significance. The direct ratio measurement is a simple and appropriate way to obtain a site-specific suppression factor without relying on detailed geological simulation, and the cancellation of detector-efficiency and acceptance terms that are constant between runs is a genuine strength. The angular distributions and the full-sky slant-depth map make the topographic effect directly visible, and the radon measurement is a useful auxiliary datum for site evaluation. If the rate-dependent systematic discussed below is quantified, the result would be a useful addition to the sparse literature on shallow and intermediate underground sites. At present, however, the headline precision is not demonstrated because the high-rate TAU run is not checked for dead time, pileup, or accidental coincidences.

major comments (3)
  1. [§4, Table 2] The central suppression factor is defined as the ratio of the TAU rate (3.80 ± 0.04 × 10^1 s^-1) to the average KY rate (8.535 × 10^-3 s^-1), but no dead-time, pileup, or accidental-coincidence correction is reported for the TAU run. Rate-dependent losses do not cancel in the TAU/KY ratio because the trigger rates differ by more than three orders of magnitude; a 2% trigger loss at TAU changes the suppression factor by about 90, which is outside the quoted ±77 statistical uncertainty. The text explicitly reports "only the statistical error here," so the claim of 4456 ± 77 is not yet demonstrated at the stated precision. Please use the stored TAU triggers or waveforms to measure dead time and check rate linearity, or add a quantitative conservative systematic uncertainty.
  2. [§4, correlated-muon sentence] The sentence claiming that correlated muons "can only increase the inferred shielding" is unclear and appears to contradict the preceding multiplicity statement. If two or more muons arriving together are counted as a single trigger, the measured TAU rate is an underestimate of the true muon arrival rate, which would reduce the measured suppression factor rather than increase it. Please clarify the logic and, if multi-muon events are intended to be a correction, provide a quantitative estimate of their fraction at TAU.
  3. [§4, Eq. (1)] The effective overburden of 873 m.w.e. is obtained by inverting Eq. (1), but the cited Mei-Hime relation is stated to be appropriate for 1–10 km.w.e., and 873 m.w.e. lies below that range. Extrapolating the formula outside its stated validity could bias the inferred depth; please justify the extrapolation or use a depth-intensity relation validated at shallow depths. Also clarify whether the quoted 873 m.w.e. depends on the rock-density assumption (2.6 g cm^-3) used for the m.w.e. conversion in Fig. 2.
minor comments (4)
  1. [Abstract and §4] The flux value is written as "3.75 ± 0.06 × 10^-6 cm^-2 s^-1" in both the abstract and Section 4; please parenthesize the uncertainty as (3.75 ± 0.06) × 10^-6 cm^-2 s^-1 to avoid ambiguity.
  2. [§4 and Fig. 10] The text says the muon shadow of the mountain is visible "in the western direction," while the Fig. 10 caption describes an eastward bias in the W-E orientation; please make this consistent.
  3. [§4, Fig. 11] Please state explicitly that the "faulty" events excluded from the angular distributions are nevertheless included in the trigger-rate counts used for the suppression factor, since the rate calculation is based on all triggers.
  4. [Throughout] There are several typographical and formatting issues, including "Tel A viv" in the author affiliations, "T able" in table captions, "auxillary" in Table 3, and "Galille" in Section 1; these should be corrected.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the suppression factor is a directly measured rate ratio, the m.w.e. conversion uses an external empirical function, and self-citations are not load-bearing.

full rationale

The paper's central claim (4456 +/- 77 suppression, 3.75e-6 cm^-2 s^-1) is a measured ratio of trigger rates at TAU and KY (Table 2), not the output of a fitted model. The conversion to an equivalent vertical depth uses the external Mei-Hime intensity function (Eq. 1, ref [19]), an independent empirical benchmark whose parameters are not fit to this dataset; agreement with the simplified simulation (approximately 860 m.w.e.) is a consistency check, not an input. The sea-level flux normalization (1.67e-2 cm^-2 s^-1) likewise comes from PDG [18]. No load-bearing argument reduces to a self-citation: references [16] and [17] describe the scintillator hardware, and [24] is an application example, not evidence for the flux result. The paper explicitly reports only statistical errors and leaves rate-dependent systematics (dead time, pileup) unquantified; that is a correctness or robustness limitation, not circularity, because the quantity quoted remains a direct measurement rather than a quantity constructed from its own assumptions. No fitted parameter is renamed as a prediction, and no uniqueness theorem or ansatz is imported from the authors' prior work.

Assumptions & free parameters 1 free parameters · 5 assumptions · 0 invented entities

The central suppression factor is a direct ratio of measured trigger rates and does not depend on fitted parameters. The conversion to absolute flux and to m.w.e. relies on external empirical inputs and a hand-picked rock density, while the detection assumptions about background and rate-independent efficiency are stated or implicit rather than demonstrated.

free parameters (1)
  • Rock density for m.w.e. conversion = 2.6 g cm^-3
    A representative rock density chosen by hand to convert geometric overburden to meters water equivalent in Figure 2 and the simulation; it affects the effective depth estimate but not the raw suppression factor.
assumptions (5)
  • domain assumption Sea-level muon flux of 1.67 x 10^-2 cm^-2 s^-1 from PDG is accurate for the TAU site, neglecting a small 44 m elevation deviation.
    Used in Section 4 to convert the measured suppression ratio into an absolute underground flux.
  • domain assumption Detector efficiency, acceptance, and trigger behavior are identical at TAU and KY and therefore cancel in the rate ratio.
    Stated in Section 4; it assumes no rate-dependent dead time or other environmental difference between the high-rate above-ground run and the low-rate underground runs.
  • domain assumption The underground trigger rate contains no significant accidental coincidence or radioactive background, so no background subtraction is needed.
    Invoked implicitly in Section 4 when interpreting all triggers as muons; no measurement of accidental rates is reported.
  • domain assumption The Mei-Hime intensity function in Eq. (1) is valid at the derived depth of roughly 873 m.w.e., even though the paper notes its stated range is 1 to 10 km.w.e.
    Used in Section 4 to convert the measured flux to an equivalent vertical depth; 873 m.w.e. is below the stated range.
  • domain assumption The simulation using the Gaisser muon spectrum and continuous energy loss model adequately describes the site's topography and effective overburden.
    Used in Section 2 to produce the 860 m.w.e. comparison value; no simulation code or parameter details are provided.

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Cite this review

Pith. "Pith review of Atmospheric muon flux suppression at potential new low-radiation underground physics laboratory in Israel." pith.science (2026). https://pith.science/paper/5IQNOCYS

@misc{pith2026250415102,
  author       = {Pith},
  title        = {Pith review of: Atmospheric muon flux suppression at potential new low-radiation underground physics laboratory in Israel},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/5IQNOCYS}},
  note         = {Machine review of arXiv:2504.15102}
}
abstract

The residual atmospheric muon flux was measured at a candidate site for a new underground, low-radiation physics laboratory beneath the Kokhav HaYarden national park in Israel. Located inside the tunnels of a hydroelectric pumped-storage facility operating since 2024, the proposed site benefits from a vertical rock overburden of 361 meters, large potential floorspace, and easy access by road. A muon hodoscope of vertically stacked wide-area $144 \times 60 \times 1.2 $ cm$^3$ plastic scintillator plates was employed to measure the suppression in the integrated muon flux at the site as compared with above ground at sea level. Data-taking took place in mid-August of 2024 for several days and was split into South-North and West-East orientations to account for the directional acceptances due to the geometry of the detector. The suppression factor is reported at $4456 \pm 77$, expressed as $3.75 \pm 0.06 \times 10^{-6}$ cm$^{-2}$ s$^{-1}$ in absolute terms, corresponding to an effective overburden of roughly $873$ m.w.e.. A deeper location at the site may also be available, but it could not be reached at this time. Furthermore, the asymmetric topography of the mountain above and its muon shadow are clearly visible in the angular data. Finally, auxiliary environmental measurements recorded low background radon activity at $28.3 \pm 14.0$ Bq m$^{-3}$. The experimental campaign thus succeeded in demonstrating the viability of the site's working conditions for future scientific research.

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