{"id":"63b266db-5eb2-46b7-a3a6-4445b1bb9293","arxiv_id":"2607.24584","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Combining XENONnT, PandaX-4T, and LZ data gives the first CEνNS-based limit on invisible solar-neutrino decay, and a future xenon detector could beat dedicated solar experiments by 1 to 2 orders of magnitude.","lead":"Solar neutrinos detected by three dark matter experiments set a new limit on invisible neutrino decay, already matching a dedicated solar observatory. Future xenon detectors could improve this by one to two orders of magnitude and test both neutrino mass states.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No significant objection identified: the central CEνNS bound is robust; the flagged assumptions are either profiled, disclosed, or numerically negligible.","rationale":"The reader correctly identifies the outside-the-Sun decay assumption and the MB22m 8B flux normalization as the main soft spots. I examined both. The outside-the-Sun assumption is numerically negligible precisely in the parameter region that the analysis excludes or projects: the solar-interior contribution to the exponential suppression is at the 10^-3 level for the current bound and 10^-4 level for the future pp/EνES projections. The flux normalization is not hidden; it is profiled with a Gaussian penalty, and the paper explicitly demonstrates that the future CEνNS sensitivity is limited by this uncertainty. The simplified PandaX-4T treatment is disclosed and is not the driver of the combined result. I also checked the possible α3 component in the CEνNS channel: the ν3 fraction is a constant ~2.2% of the 8B flux and is largely absorbable by the 13.13% flux normalization, so it does not threaten the α2 bound. For the EνES projections, the ν3 event-rate fraction is tiny once the ν_e-enhanced cross section is weighted by the small |U_e3|^2 production fraction. The central claim, that current CEνNS data give the first CEνNS-based constraint on invisible solar-neutrino decay at a level comparable to SNO, is supported by a standard and internally consistent analysis. No internal inconsistency or unsupported step was found, so the verdict should remain unchanged.","tokens_in":16464,"tokens_out":22641,"duration_ms":226648,"concrete_test":"Recompute the combined α2 bound including the solar-interior decay contribution, e.g. by using an effective path length L_eff(r) = L⊙ + (R_sun - r) in the damping factors of Eq. (1) before averaging over the production density in Eq. (8). If the 90% CL bound shifts by more than about 5%, the outside-the-Sun assumption would be load-bearing.","verdict_should_be":"UNCHANGED","load_bearing_attack":"I find no load-bearing concern that would overturn the central claim. The strongest assumption, decay acting only along the Sun-Earth path (Sec. II, before Eq. (7)), is quantitatively safe for the derived bounds. For α2 = 1.2e-11 eV2 and Eν ≈ 10 MeV, decay over the solar interior contributes α2 L_sun/Eν ≈ 4e-3 to the exponent, compared with ≈ 0.76 over the Sun-Earth baseline; for the future pp/EνES bounds (α1 ≈ 8e-15 eV2, Eν ≈ 0.3 MeV) the interior contribution is ≈ 1e-4. Thus Eq. (7) is valid within the allowed region. The 8B flux normalization is explicitly profiled with a 13.13% Gaussian penalty in Eq. (27), and the paper shows that the future CEνNS sensitivity saturates unless this uncertainty is reduced. The simplified PandaX-4T treatment is acknowledged and does not drive the combined bound. The projected XLZD EνES sensitivities are clearly labeled as sensitivity studies rather than constraints. I therefore see no reason to change the reader's ACCEPT verdict.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper derives constraints on invisible neutrino decay from solar neutrinos using CEνNS data from XENONnT, PandaX-4T, and LZ. The combined analysis yields α2 < 1.2×10^-11 eV² at 90% CL (Eq. 28), stated as the first CEνNS-based constraint and comparable in strength to the SNO bound. The authors then project the reach of a future XLZD observatory via CEνNS (α2 ~ 3×10^-12 eV²) and via EνES from pp neutrinos (α1 < 7.9×10^-15 eV² and α2 < 3.0×10^-14 eV² at 90% CL), emphasizing that the 8B flux normalization is the limiting systematic for the former and that the latter could surpass dedicated solar-neutrino bounds by one to two orders of magnitude.","tokens_in":16659,"tokens_out":14496,"duration_ms":141035,"significance":"The central result is physically well motivated: the CEνNS channel is flavor-blind, solar 8B neutrinos arrive predominantly as ν2, and the Sun-Earth baseline is long enough to make decay competitive with SNO. The analysis uses public data releases, the XENONnT 4D response matrices, and profiles explicit nuisance parameters for fluxes and backgrounds; the XLZD results are appropriately presented as sensitivity studies rather than constraints. I checked the main assumption in Sec. II before Eq. (7): for the derived α2 bound, the solar-interior contribution to the damping exponent is about 4×10^-3 compared with about 0.76 over the Sun-Earth baseline, so neglecting decay inside the Sun is quantitatively safe. If correct, this is the first CEνNS-based probe of invisible solar-neutrino decay and opens a new, complementary detection channel.","major_comments":[],"minor_comments":[{"comment":"Please clarify whether the per-bin correction factors c_i are fixed from a SM best-fit or profiled in the χ²; if profiled together with α2, they would absorb the decay-induced deficit and erase the PandaX sensitivity. The paper's central conclusion is not affected because PandaX alone yields no bound and the combined result is driven by XENONnT and LZ, but the procedure should be stated explicitly.","section":"Sec. III A, Eq. (19)"},{"comment":"The index i is used both for the bin and for the sum over background components; use a separate index (e.g., k) for the backgrounds so that the expression reads N_i = R_i(1+γ) + Σ_k B_{i,k}(1+β_k).","section":"Eq. (26)"},{"comment":"The text 'only US2' should read 'only S2'.","section":"Sec. III A"},{"comment":"There is a duplicated 'the' in 'driven by the the Super-Kamiokande data'.","section":"Sec. I"},{"comment":"Consider adding a footnote that '—' for PandaX-4T means no significant bound from this dataset alone, for consistency with Sec. IV A.","section":"Table I"}],"recommendation":"minor_revision","confidential_remarks":"The manuscript is within the journal's scope and the novelty is clear. Some of the analysis infrastructure is carried over from the authors' previous work (e.g., Refs. [58,60,64,72,73]), but those papers are cited and the decay interpretation is new. I do not see a need for additional scrutiny beyond the standard process."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The main thing to know: this paper delivers the first data-driven constraint on invisible solar neutrino decay using CEνNS from running dark matter experiments, and the bound is believable. Combining XENONnT, PandaX-4T, and LZ nuclear-recoil data, they get α2 < 1.2×10^-11 eV2 at 90% CL, within a factor of ~1.5 of the SNO bound. The analysis is careful and, as far as I can tell, standard: they use the public XENONnT 4D response matrices, profile the 8B flux normalization with the MB22m 13.13% uncertainty, and handle LZ and PandaX with documented simplifications. The future XLZD projections are labeled as sensitivity studies, not constraints, and the EνES reach for α1 and α2 is consistent with earlier work by Huang-Zhou and Martínez-Miravé et al.\n\nWhat deserves credit: the central claim is not circular. The damping formula is taken from the literature, the decay parameter is fit to external data, and the paper explicitly shows that the 8B flux uncertainty, not statistics, will limit future CEνNS sensitivity. That is a useful, honest quantitative point. The paper also correctly notes the complementarity between CEνNS (α2 only) and EνES (α1 and α2), which is a nice tie-in for future detectors.\n\nSoft spots, in proportion. The PandaX-4T treatment is admittedly simplified, with per-bin correction factors c_i tuned to the collaboration's best-fit spectrum. That weakens the PandaX-only bound, but it does not drive the combined result, so it is a minor issue. The assumption that decay occurs only along the Sun–Earth path, not inside the Sun, is disclosed and standard in the literature; the stress-test note quantifies that the interior contribution is negligible in the allowed region, and I agree. The LZ data show a slight deficit, which shifts the profile and weakens the bound; Appendix B handles this transparently. I would have liked to see the code or likelihoods released, but the use of public data releases and response matrices largely mitigates that concern.\n\nCitation pattern: there is unavoidable overlap with the authors' own prior work on CEνNS analysis (Refs. [58,60,64]), but the new decay-specific content is clearly separated and the prior-work citations are appropriate. No self-citation inflation.\n\nWho is this for? Anyone working on neutrino decay, solar neutrinos, or the physics reach of dark matter detectors. It is a solid, incremental but genuinely new result, not a breakthrough. It deserves a serious referee: the analysis is reproducible in principle, the claim is appropriately scoped, and the conclusions follow from the equations. Send it to review.\n\nRecommendation: accept after minor revision, mainly requesting code release and a slightly deeper discussion of the PandaX c_i factors.","headline":"Solid first CEνNS-based constraint on invisible solar neutrino decay from current dark matter data; the central bound holds up and the projections are clearly labeled.","tokens_in":17307,"tokens_out":1034,"would_cite":true,"duration_ms":11094,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Invisible decay of solar neutrinos is constrained for the first time using coherent scattering data from dark matter experiments.","keywords":["invisible neutrino decay","solar neutrinos","coherent elastic neutrino-nucleus scattering","dark matter direct detection","XENONnT","PandaX-4T","LUX-ZEPLIN","XLZD"],"falsifier":"A pp-neutrino EνES measurement at a future detector that recovers the full standard solar model pp flux with no energy-dependent suppression would falsify the α2 bound, because the same α2 ~ $10^{-11}$ eV² would suppress the low-energy pp flux much more strongly than the few-percent effect seen at 8B energies.","tokens_in":16227,"feed_emoji":"☀️","tokens_out":9920,"duration_ms":75653,"temperature":0.7,"pith_summary":"Solar neutrinos spend about eight minutes traveling from the Sun to the Earth at energies from a few hundred keV to several MeV, making them sensitive probes of invisible decay: any decay of a neutrino mass eigenstate suppresses the flux by a factor exp(-α_i L/Eν). The paper applies this idea to the coherent elastic neutrino-nucleus scattering (CEνNS) data of the dark matter experiments XENONnT, PandaX-4T, and LZ, and obtains a first constraint α2 < 1.2×$10^{-11}$ eV² at 90% CL on the decay parameter of the ν2 state. This is already comparable to the SNO bound, even though these detectors were built to search for dark matter. The paper then projects that a future xenon observatory could improve this by an order of magnitude through CEνNS, and that electron-recoil measurements of pp neutrinos could reach α1 < 7.9×$10^{-15}$ eV² and α2 < 3.0×$10^{-14}$ eV², surpassing dedicated solar-neutrino experiments by one to two orders of magnitude.","feed_headline":"Dark matter detectors now bound invisible neutrino decay","feed_subtitle":"The same detectors that hunt dark matter can test whether neutrinos decay en route from the Sun.","key_machinery":"The central object is the decay parameter α_i = m_i/τ_i of each neutrino mass eigenstate, which controls the invisible-decay damping factor D_i(Eν,L) = exp(-α_i L/Eν) in the solar neutrino flux. At high energies (8B neutrinos, above roughly 7 MeV) the MSW effect and solar matter make the arriving flux almost pure ν2, so CEνNS data are sensitive to α2 alone; at low energies (pp neutrinos, below roughly 0.4 MeV) the flux is a mixture of ν1 and ν2, enabling EνES measurements to constrain α1 and α2. The analysis machinery is a binned χ² likelihood that treats the solar flux normalization and detector backgrounds as nuisance parameters, with the unoscillated fluxes from the MB22m standard solar model.","core_discovery":"The central discovery the authors claim is that the solar-neutrino CEνNS signals already observed at dark matter direct detection experiments carry a measurable imprint of invisible neutrino decay, and that the combined fit to XENONnT, PandaX-4T, and LZ data bounds the ν2 decay parameter to α2 < 1.2×$10^{-11}$ eV² at 90% CL. This bound is comparable to the SNO constraint α2 < 8.1×$10^{-12}$ eV², but it comes from a completely independent detection channel. The paper derives this by computing the oscillation probabilities for 8B neutrinos with a damping term exp(-α_i L/Eν) applied along the Sun–Earth baseline, and by profiling the 8B flux normalization in the likelihood. It also establishes that the same method at the future XLZD observatory, using both nuclear recoils and electron recoils from pp neutrinos, could reach α1 < 7.9×$10^{-15}$ eV² and α2 < 3.0×$10^{-14}$ eV² at 90% CL—one to two orders of magnitude beyond the current dedicated solar-neutrino limits.","pith_inferences":["If the current α2 bound holds, dark matter detectors have effectively become solar-neutrino decay observatories, and any future exposure increase with the same background model will keep improving the limit until the solar flux uncertainty dominates.","The 8B flux normalization is the limiting systematic, so an independent high-precision measurement of the 8B flux—by an experiment not relying on CEνNS event rates—would directly sharpen the decay constraint.","The same exp(-α_i L/Eν) logic applies to any long-baseline low-energy neutrino source, so the technique could be extended to supernova neutrinos or future long-baseline reactor experiments, though those sources have different L/Eν windows.","A detection of an energy-dependent deficit in the pp flux would be a strong invisible-decay signal, but it would also require ruling out other new physics that mimics a 1/Eν suppression, such as energy-dependent non-standard neutrino interactions."],"forward_implications":["The combined CEνNS bound α2 < 1.2×10^-11 eV² is the first of its kind from solar-neutrino coherent scattering and is already competitive with the SNO result.","With current 8B flux uncertainties, future CEνNS sensitivity saturates near 3–4×10^-12 eV² regardless of exposure; reducing the flux uncertainty would improve the bound by roughly a factor of two.","At XLZD, the EνES channel from pp neutrinos could constrain α1 < 7.9×10^-15 eV² and α2 < 3.0×10^-14 eV², beating dedicated solar-neutrino experiments by one to two orders of magnitude.","If a deficit appears in the pp flux via EνES, an independent CEνNS measurement would determine whether the deficit comes from ν2 decay or ν1 decay."],"supporting_citations":[{"why":"Supplies the SNO limit α2 < 8.1×10^-12 eV² to which the new CEνNS bound is compared.","marker":"[23]"},{"why":"Provides the XENONnT CEνNS data (SR0+SR1+SR2) that drive the strongest current bound.","marker":"[52]"},{"why":"Provides the PandaX-4T CEνNS solar-neutrino data included in the combined analysis.","marker":"[53]"},{"why":"Provides the LZ CEνNS solar-neutrino data included in the combined analysis.","marker":"[54]"},{"why":"Defines the XLZD detector parameters and nominal exposures used for future projections.","marker":"[67]"},{"why":"Supplies the MB22m standard solar model fluxes and their uncertainties for pp and 8B neutrinos.","marker":"[88, 89]"},{"why":"Sets the framework for the XLZD EνES electron-recoil sensitivity analysis.","marker":"[72, 73]"},{"why":"Provides earlier projections for solar-neutrino decay sensitivity that the EνES results are compared against.","marker":"[35]"}],"fun_headline_variants":["Dark matter detectors place first bound on solar neutrino decay","Invisible solar neutrino decay constrained by dark matter detectors","Dark matter experiments tighten limits on invisible neutrino decay","First solar neutrino decay bound from dark matter lab data"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The analysis assumes that invisible neutrino decay occurs only after the neutrinos leave the Sun, so the damping factor uses the full Sun–Earth distance and no decay or regeneration happens inside the solar interior.","fun_headline_variants_meta":{"raw":{"variants":["Dark matter detectors place first bound on solar neutrino decay","Invisible solar neutrino decay constrained by dark matter detectors","Dark matter experiments tighten limits on invisible neutrino decay","First solar neutrino decay bound from dark matter lab data"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000633,"raw_usage":{"total_tokens":2956,"prompt_tokens":1012,"completion_tokens":1944,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":628,"completion_tokens_details":{"reasoning_tokens":1882}},"tokens_in":628,"tokens_out":1944,"duration_ms":15793,"temperature":1.0,"reasoning_tokens":1882,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T15:27:05.564471+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A pp-neutrino EνES measurement at a future detector that recovers the full standard solar model pp flux with no energy-dependent suppression would falsify the α2 bound, because the same α2 ~ $10^{-11}$ eV² would suppress the low-energy pp flux much more strongly than the few-percent effect seen at 8B energies.","supporting_citations":[{"cited_title":"Constraints on Neutrino Lifetime from the Sudbury Neutrino Observatory","cited_arxiv_id":"1812.01088","evidence_quote":"Supplies the SNO limit α2 < 8.1×10^-12 eV² to which the new CEνNS bound is compared."}],"review_version":2}