{"id":"0abbca25-bdb1-4525-849e-c62a2ef3a43c","arxiv_id":"2411.09634","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Atmospherless bodies in the Solar System suppress cosmic-ray-induced neutrino and muon fluxes by about three to four orders of magnitude, opening new sites for ultra-low-background rare-event searches.","lead":"This paper calculates cosmic-ray-induced neutrino, muon, and gamma-ray fluxes on the Moon, asteroids, icy moons, and proposed space ice balls, finding 1,000-fold or larger reductions in the main background fluxes compared to underground sites on Earth. It suggests these low-radiation sites could host next-generation dark matter, neutrinoless double-beta decay, and supernova neutrino searches.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Prompt-component normalization is the load-bearing uncertainty: if the charm-decay parameters R_nu/R_mu are larger than assumed, the claimed ~1e3 suppression erodes near 100 TeV and the lunar muon-depth equivalence weakens.","rationale":"The reader identifies the prompt-component normalization as the weakest assumption, and I agree. The paper's Fig. 6 and the Section VI statement about unclear critical energies are explicit acknowledgments that the high-energy end of the 1e3 claim is not controlled by data. The R_nu/R_mu parameterization is a one-parameter rescaling of a low-energy atmospheric flux; it is not derived from a charm-production calculation for rock or ice targets, and the allowed range spans a factor of five in R_nu. However, the qualitative physics—short hadronic interaction lengths in solids suppressing DIF pions and kaons—is well established, and the paper provides independent support: the semi-analytic and Geant4 estimates agree between 1 GeV and 1 TeV, the Earth benchmarks are reasonable, and the DAR/DIF distinction is physically grounded. Therefore the central idea survives; what is conditional is the quantitative reach and the exact energy range of the suppression. The reader's CONDITIONAL verdict is appropriate, and my independent assessment does not change it.","tokens_in":28349,"tokens_out":14544,"duration_ms":149967,"concrete_test":"Recompute the solid-target (Moon) to atmosphere (Earth) neutrino and muon flux ratios at E = 1e3, 1e4, and 1e5 GeV using Eqs. (B28)-(B36) with R_nu = 0.1 R_nu, 0.5 R_nu, and R_nu, and with the pQCD-based prompt fluxes of Ref. [61] substituted energy-by-energy instead of via a single rescaling factor. Identify the energy E_c at which the suppression factor drops below 1e2. If E_c falls below 100 TeV for any allowed prompt parameterization, the abstract and Table II should be revised to present the suppression as an energy- and flavor-dependent function rather than a blanket '3 orders of magnitude' over the full 50 MeV-100 TeV interval.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim—a ~1e3 suppression of cosmic-ray neutrino fluxes across 50 MeV to 100 TeV—depends on the decay-in-flight (DIF) component remaining dominant over the prompt component throughout that window. The prompt contribution is modeled by rescaling the atmospheric low-energy flux with R_nu (~8e-4) and R_mu (<2e-3) in Eqs. (B33)-(B36), values adopted from Ref. [38] rather than measured. The paper's own uncertainty treatment uses R_nu between 0.1 and 0.5 R_nu, a five-fold spread, and Fig. 6 shows that the value needed to match pQCD differs in different energy ranges: 0.5 R_nu below 1e5 GeV, 0.1 R_nu above. For R_mu only an upper bound is given. Because the prompt component is unsuppressed in solids, at energies where the prompt/conventional fraction exceeds roughly 1e-2, the Moon-to-Earth neutrino ratio rises from ~1e-4 toward 1, eroding the 1e3 suppression; similarly, the 100-m lunar muon flux becomes prompt-dominated and the D_mu=1 km equivalence in Table II becomes optimistic. The paper itself concedes in Section VI that 'the exact critical energies are not clear because they depend on the not-well-constrained prompt component.' Thus the headline suppression factor is not established across the full claimed energy interval, and the upper end near 1e5 GeV carries the largest unquantified risk. The qualitative reduction in DIF backgrounds is robust; what is at risk is the specific 'three orders of magnitude over 50 MeV-100 TeV' formulation and the muon-depth equivalence.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript studies cosmic-ray-induced neutrino, muon, and gamma-ray fluxes in atmosphere-less Solar System bodies (the Moon, Mars, asteroids, Europa, Rhea, comets, and a human-made ice ball) using both semi-analytic transport calculations and Geant4 Monte Carlo simulations. It claims that in such bodies the decay-in-flight component of cosmic-ray secondaries is strongly suppressed, so that neutrino fluxes are reduced by up to about three orders of magnitude relative to deep underground on Earth over a broad energy range, and muon fluxes at shallow depth on the Moon are equivalent to those at about 1 km depth on Earth. The paper also discusses solar-neutrino suppression with distance from the Sun, natural radioactivity in candidate sites, and proposes a near-term lunar lava-tube measurement of muon and gamma fluxes as a way to constrain the prompt cosmic-ray component. The central physics argument is that a solid target, unlike a gas, suppresses pion/kaon decay-in-flight while leaving charmed-hadron decays (the prompt component) unsuppressed, so that the prompt component eventually dominates at high energies.","tokens_in":28735,"tokens_out":4404,"duration_ms":44723,"significance":"If the quantitative claims hold, this paper identifies qualitatively new opportunities for rare-event searches: WIMP direct detection, neutrinoless double-beta decay, and supernova-neutrino detection would face cosmic-ray-induced backgrounds far smaller than those in terrestrial underground laboratories. The combination of independent semi-analytic and Monte Carlo methods, with an Earth benchmark that reproduces measured muon fluxes to 30--40%, is a genuine strength, as is the explicit discussion of the prompt component's role and of its large uncertainty. The paper also gives a concrete and falsifiable near-term target: a measurement of muon and gamma fluxes in the Mare Tranquillitatis Pit. The main significance is therefore conceptual and programmatic rather than a precise quantitative prediction, and the usefulness of the paper for future mission planning depends on whether the claimed suppression factors are stated with their energy-dependent uncertainties.","major_comments":[{"comment":"The headline claim that cosmic-ray neutrino fluxes between 50 MeV and 100 TeV are suppressed by about three orders of magnitude is not established at the upper end of that interval. The prompt component is parameterized through R_nu and R_mu adopted from Ref. [38] (Eqs. B33--B36) rather than measured, and Fig. 6 shows that no single R_nu reproduces the pQCD band across the full energy range: R_nu = 0.5 Rbar_nu is favored below about 10^5 GeV, while R_nu = 0.1 Rbar_nu is favored above. Because the prompt component is unsuppressed in solids, the lunar and ice-ball neutrino fluxes rise toward the atmospheric flux as E_nu approaches 10^5--10^7 GeV, and Section VI itself states that the exact critical energies are unclear. I ask the authors to show the suppression factor as an explicit function of E_nu for the full adopted R_nu range (including the pQCD comparison) and to restate the 50 MeV--100 TeV claim with this energy-dependent caveat.","section":"Section VI and Fig. 3; Section III and Appendix B.2"},{"comment":"The claimed suppression range is internally inconsistent for the low-energy part of the quoted interval. Table II assigns the whole 50 MeV < E_nu < 100 TeV band to the 'mid-energy' category with a suppression factor of 10^3, while Section VI states that at low energy the total neutrino flux is not substantially suppressed and that only the electron-antineutrino flux is suppressed by a factor of about 10 after oscillations. The DAR-dominated region below roughly 100 MeV therefore does not share the three-orders-of-magnitude suppression claimed for the DIF-dominated band. The abstract and Table II should be reworded so that the 10^3 suppression is attributed only to the mid-energy DIF-dominated range, with the low-energy DAR region reported separately.","section":"Table II and Section VI"},{"comment":"The muon-depth equivalence D_mu (for example, 100 m on the Moon equivalent to about 1 km on Earth) depends directly on the unmeasured prompt-muon normalization. The paper sets R_mu at its maximum, Rbar_mu, for this estimate, and notes that R_mu is only bounded from above. Since at roughly 100 m depth in the Moon the muon flux is prompt-dominated when R_mu is near its maximum, the quoted D_mu is an upper-limit-based projection rather than a central prediction. The authors should show D_mu as a function of R_mu, or at least give separate D_mu values for R_mu = 0 and R_mu = Rbar_mu, and state clearly how the equivalence depends on this parameter.","section":"Section IV, Fig. 4, and Table II"}],"minor_comments":[{"comment":"The word 'researcgers' in the first paragraph appears to be a typo for 'researchers'.","section":"Section I"},{"comment":"The sentence describing Rhea, 'recently found to like be comprised of mostly ice', appears to be missing a word; it should likely read 'recently found to likely be comprised of mostly ice'.","section":"Section IV"},{"comment":"The notation Rnu and Rmu is used inconsistently: the text sometimes writes R_nu = 0.1 - 0.5Rnu and R_mu = R_mu, where the bar over the symbol is essential to distinguish the reference value from the varied parameter. The table and figure captions should use a consistent notation such as Rbar_nu and Rbar_mu.","section":"Table II and Section III"},{"comment":"The units 'MeV g −1 cm2' should be typeset consistently as 'MeV g^{-1} cm^2' throughout the appendix and Section III.","section":"Appendix B.3"},{"comment":"The Monte Carlo results fall below the semi-analytic muon fluxes by about a factor of two at the depths of experimental interest, as the authors acknowledge; this systematic discrepancy, together with the 30--40% Earth-surface benchmark, should be stated as an explicit uncertainty band in the figures that are used for the depth-equivalence claims.","section":"Section IV and Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The stress-test concern about the prompt component is confirmed by the manuscript's own Fig. 6 and by the Section VI caveat that the critical energies are not well constrained. The qualitative conclusion (strong suppression of decay-in-flight backgrounds in atmosphere-less bodies) is robust, but the quantitative headline and the Table II entries need to be re-scoped with energy-resolved uncertainties. I do not see grounds for rejection if the authors provide that treatment; the paper is a valuable conceptual and programmatic contribution to the rare-event-search community."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Worth a careful read if you have any stake in the future of rare-event searches. The paper's real contribution is a first combined semi-analytic/Monte Carlo estimate of muon, neutrino, and gamma backgrounds at atmosphere-less Solar System sites, with the Earth benchmark built in. The two methods agree well between 1 GeV and 1 TeV, and the Earth benchmark reproduces measured muon fluxes to 30-40%, which is respectable for this kind of transport calculation. The low-energy part, including decay-at-rest neutrinos and flavour oscillation, is genuinely new compared with the 1980s lunar neutrino papers. The identification of the lunar lava tube at Mare Tranquillitatis as a near-term site to measure the prompt component is a good concrete proposal.\n\nThe soft spot is exactly where the stress test points: the prompt component. The paper parameterizes prompt charm contributions with R_nu and R_mu adopted from Ref. [38], not measured, and Fig. 6 shows that different values are needed to match pQCD below and above 1e5 GeV. The paper itself concedes the critical energies are not clear because the prompt component is not well constrained. So the '10^3 suppression up to 100 TeV' headline is not established on the upper end. For the energy range that matters for most near-term experiments (WIMP, 0vbb, DSN below tens of MeV), the qualitative suppression is solid; the uncertainties are quantitative. The simulations also lack primaries above 30 TeV and underpredict deep muon fluxes by about a factor of two, and Table II has no propagated uncertainties. Those are minor-to-moderate issues, not fatal.\n\nI don't see circularity. The transport formalism and parameters come from the standard literature, and the benchmarking is against measured fluxes, not against the target outputs.\n\nWho is this for? Anyone thinking about long-term strategies for neutrino-fog avoidance, lunar science, or experimental particle physics in space. It deserves a serious referee. I would accept for review and ask for a quantitative uncertainty band on the prompt component, a propagation of that uncertainty into Table II, and a release of the simulation code and data.","headline":"A solid scoping study whose qualitative suppression result is robust, but whose 'three orders of magnitude up to 100 TeV' headline overreaches on the prompt component; it deserves review.","tokens_in":29248,"tokens_out":2041,"would_cite":false,"duration_ms":20822,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper claims that airless Solar System bodies suppress cosmic-ray-induced neutrino and muon fluxes by up to three orders of magnitude, opening new low-background sites for rare-event searches.","keywords":["cosmic-ray neutrinos","muon flux","underground rare-event searches","WIMP dark matter","neutrinoless double-beta decay","diffuse supernova neutrinos","prompt component","lunar lava tubes"],"falsifier":"Measure the muon flux versus depth inside a lunar lava tube with roughly 100 m of overburden: if the flux matches the paper's curve at about one-thousandth of Earth's atmospheric-muon level, the suppression claim is confirmed, whereas a flux even a factor of a few higher at shallow depths would indicate a larger prompt component and a smaller usable energy window.","tokens_in":28118,"feed_emoji":"🌑","tokens_out":6160,"duration_ms":59363,"temperature":0.7,"pith_summary":"This paper argues that the quietest places in the Solar System for rare-event physics are not deep underground on Earth but just ~100 m below the surface of airless bodies like the Moon. Because solid rock stops charged pions and kaons before they can decay, the cosmic-ray decay-in-flight neutrinos and muons that dominate backgrounds in terrestrial laboratories are suppressed by roughly a factor of $10^{3}$ for neutrino energies between 50 MeV and 100 TeV. Muons at 100 m depth on the Moon are estimated to be as rare as muons at ~1 km depth on Earth, and the irreducible neutrino-induced muon floor is also much lower. The authors conclude that WIMP dark-matter searches, neutrinoless double-$\\beta$ decay, and supernova-neutrino detectors could reach sensitivities that are impractical on Earth, with a lunar lava-tube measurement of muons and gamma rays as a near-term first step.","feed_headline":"Airless moons cut cosmic-ray neutrino background 1,000-fold","feed_subtitle":"Shallow lunar caves could host dark-matter and double-beta searches at deep-lab background levels.","key_machinery":"The load-bearing mechanism is the competition between a charged meson's decay length and its interaction or stopping length in the medium, captured by the transport equations in Section III and Fig. 2. In Earth's gas the decay lengths of GeV to TeV pions and kaons are shorter than their stopping or interaction lengths, so decay-in-flight dominates; in a solid the hierarchy reverses and those mesons mostly interact or stop before decaying, leaving only low-energy decay-at-rest neutrinos and an unsuppressed high-energy prompt component from ultra-short-lived charmed hadrons. The prompt component is parameterized by rescaling the atmospheric low-energy flux with factors R_nu of order 8 x $10^{-4}$ and R_mu below 2 x $10^{-3}$, and it sets the floor on how much the high-energy background can be reduced.","core_discovery":"On the paper's own terms, the central discovery is that the absence of an atmosphere turns the dominant cosmic-ray background production mechanism off. In Earth's air, pion and kaon decay lengths are shorter than their interaction or stopping lengths over a broad energy range, so decay-in-flight produces abundant muons and neutrinos; in a solid body the hierarchy reverses and those mesons mostly interact or stop before decaying. The result is a cosmic-ray-induced neutrino flux in the 50 MeV to 100 TeV range that is roughly $10^{3}$ lower than at the deepest terrestrial sites even at shallow depths, and an underground muon flux at about 100 m on the Moon equivalent to about 1 km depth on Earth. The semi-analytic calculations and Geant4 Monte Carlo simulations agree well between 1 GeV and 1 TeV, while the suppression saturates at a reduced neutrino-induced muon floor and the low-energy decay-at-rest neutrino flux and high-energy prompt component from charmed hadrons remain, with the prompt component limiting the gain at the highest energies.","pith_inferences":["The paper's suppression factors assume the prompt charm component is near its estimated value; if prompt production is actually larger at energies below about 100 TeV, the practical gain in the upper part of the 50 MeV to 100 TeV window shrinks, and a lunar muon-versus-depth measurement could settle which case is realized.","Because the muon floor scales inversely with surface density, a compact metallic asteroid at the same depth would have an even lower irreducible muon background than an ice body, an extension the paper's own scaling argument implies but does not state.","The same background logic applies to future long-baseline neutrino detectors at the Moon, whose large attenuation lengths would benefit directly from the suppressed atmospheric neutrino flux in the medium-energy range.","If Europa's sub-ice ocean is as radiochemically clean as seawater measurements suggest, its liquid water offers a nearly zero-radiogenic environment for a future rare-event detector, leaving the solar neutrino flux at one twenty-fifth of Earth's value as the dominant background."],"forward_implications":["WIMP dark-matter and neutrinoless double-beta decay searches in a roughly 100 m deep lunar lava tube would face cosmic-ray-induced backgrounds similar to those in the deepest terrestrial laboratories, without needing kilometers of rock.","A lunar detector could observe the diffuse supernova neutrino background in the tens-of-MeV range with roughly an order of magnitude better sensitivity to electron antineutrinos than Earth-based estimates, after accounting for neutrino flavor oscillation.","Solar-neutrino backgrounds shrink as the inverse square of distance from the Sun, so ice-ball or outer-moon sites reduce the neutrino fog that limits dark-matter experiments.","The neutrino-induced muon floor, the minimum underground muon flux, is about 10^3 times lower on the Moon than on Earth because it inherits the suppressed medium-energy neutrino flux.","A first measurement of the prompt muon component and gamma rays at the Mare Tranquillitatis Pit would constrain both cosmic-ray particle production and lunar thermal and evolution models."],"supporting_citations":[{"why":"Supplies the transport formalism, the decay-in-flight versus decay-at-rest channel decomposition, and the R_nu and R_mu rescaling values that parameterize the prompt component.","marker":"[38]"},{"why":"Provides the recommended terrestrial atmospheric neutrino flux against which the Earth calculation is benchmarked.","marker":"[58]"},{"why":"Gives the perturbative-QCD prompt neutrino flux used to bracket the R_nu range for the semi-analytic predictions.","marker":"[61]"},{"why":"The leading neutrino telescope's prompt-flux upper limit is the experimental check that the chosen prompt parameterization must satisfy.","marker":"[62]"},{"why":"Earlier lunar neutrino simulation whose inferred lunar fluxes the paper compares with and disagrees with in Section VII.","marker":"[13]"},{"why":"The dark-matter background study built on that earlier simulation, which the paper's larger Moon-to-Earth neutrino flux ratios would revise.","marker":"[37]"},{"why":"Reports the Mare Tranquillitatis Pit overburden that makes the near-term lunar muon and gamma-ray measurement concretely feasible.","marker":"[44]"},{"why":"Demonstrates that dense material stops pions before decay, the same physics that suppresses decay-in-flight neutrinos in solid bodies.","marker":"[39]"}],"fun_headline_variants":["Moon caves slash neutrino noise 1000x for rare searches","Airless worlds offer cosmic-ray quiet for deep physics","Lunar pits could host ultra-quiet physics labs","Shallow moon digs rival deep Earth labs for dark matter"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole gain rests on the prompt component from charmed-hadron decays being as small as the paper assumes; if that component is substantially larger around 100 TeV and below, the claimed neutrino suppression and the deep muon floor would both weaken.","fun_headline_variants_meta":{"raw":{"variants":["Moon caves slash neutrino noise 1000x for rare searches","Airless worlds offer cosmic-ray quiet for deep physics","Lunar pits could host ultra-quiet physics labs","Shallow moon digs rival deep Earth labs for dark matter"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000179,"raw_usage":{"total_tokens":1315,"prompt_tokens":977,"completion_tokens":338,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":593,"completion_tokens_details":{"reasoning_tokens":272}},"tokens_in":593,"tokens_out":338,"duration_ms":4615,"temperature":1.0,"reasoning_tokens":272,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T20:25:43.615162+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the muon flux versus depth inside a lunar lava tube with roughly 100 m of overburden: if the flux matches the paper's curve at about one-thousandth of Earth's atmospheric-muon level, the suppression claim is confirmed, whereas a flux even a factor of a few higher at shallow depths would indicate a larger prompt component and a smaller usable energy window.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the transport formalism, the decay-in-flight versus decay-at-rest channel decomposition, and the R_nu and R_mu rescaling values that parameterize the prompt component."},{"cited_title":"Lignell and M","cited_arxiv_id":null,"evidence_quote":"Provides the recommended terrestrial atmospheric neutrino flux against which the Earth calculation is benchmarked."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The dark-matter background study built on that earlier simulation, which the paper's larger Moon-to-Earth neutrino flux ratios would revise."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates that dense material stops pions before decay, the same physics that suppresses decay-in-flight neutrinos in solid bodies."}],"review_version":1}