{
  "slug": "where-the-missing-neutrons-could-go",
  "title": "Where the Missing Neutrons Could Go",
  "href": "/strata/where-the-missing-neutrons-could-go/",
  "field": "particle physics",
  "claim": {
    "statement": "We propose to explain this anomaly by a dark decay channel for the neutron, involving one or more dark sector particles in the final state.",
    "claimants": "Bartosz Fornal and Benjamín Grinstein",
    "citation": "Bartosz Fornal and Benjamín Grinstein (2018), Dark Matter Interpretation of the Neutron Decay Anomaly, Physical Review Letters 120, 191801. DOI: 10.1103/PhysRevLett.120.191801. Numerical version: arXiv:1801.01124v3.",
    "year": 2018,
    "headline_as_printed": "879.6 ± 0.6 s (bottle); 888.0 ± 2.0 s (beam); Δτ_n ≃ 8.4 s; 4.0 σ; Br(n → p + anything) ≈ 99%; approximately 1% dark branch."
  },
  "records": [
    {
      "file": "claimant-summary.json",
      "role": "claimant-data",
      "name": "Historical claimant summary",
      "url": "https://arxiv.org/pdf/1801.01124v3",
      "licence": "Factual transcription. Published article CC BY 4.0; the versioned arXiv PDF has a separate non-exclusive distribution licence and is not redistributed.",
      "licence_url": "https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.191801",
      "retrieved": "2026-09-22",
      "sha256": "d53c74e39f1de928380f225753e7a01b0d9b6b248711f0a9fa62bfd6737322a5",
      "units": 4
    },
    {
      "file": "ucna-published-bound.json",
      "role": "control-data",
      "name": "UCNA published-bound factual extract",
      "url": "https://arxiv.org/pdf/1803.10890v1",
      "licence": "Independently transcribed numerical facts only. Article copyright 2018 American Physical Society. No article, figure or event data redistributed; no underlying article reuse rights granted.",
      "licence_url": "https://journals.aps.org/prc/abstract/10.1103/PhysRevC.97.052501",
      "retrieved": "2026-09-22",
      "sha256": "4f5f613a9243bee9c39da45ff039af10fd0e86b0539690c70570a2ad3a75c77c",
      "units": 1
    },
    {
      "file": "context-facts.json",
      "role": "reference",
      "name": "Attribution and versioned context facts",
      "url": "https://arxiv.org/abs/2306.11349v1",
      "licence": "Original factual annotations and bibliography; no source article, image or figure redistribution rights granted. PDG responses are supplied separately under CC BY 4.0.",
      "licence_url": "https://arxiv.org/licenses/nonexclusive-distrib/1.0/license.html",
      "retrieved": "2026-09-22",
      "sha256": "0bc4b141aa52b5acc2380797db64989a63bc1907f87b85add80bea44e8316edc",
      "units": 8
    },
    {
      "file": "pdg-info.json",
      "role": "reference",
      "name": "PDG edition metadata",
      "url": "https://pdgapi.lbl.gov/info",
      "licence": "CC BY 4.0",
      "licence_url": "https://pdgapi.lbl.gov/doc/restapi.html",
      "retrieved": "2026-09-22",
      "sha256": "273ecc5f6e1c1c8f687985a17d84f7f059c72fe4a74c5264dabe268ea30c8af7",
      "units": 1
    },
    {
      "file": "pdg-summary.json",
      "role": "reference",
      "name": "PDG neutron mean-life summary",
      "url": "https://pdgapi.lbl.gov/summaries/S017T",
      "licence": "CC BY 4.0",
      "licence_url": "https://pdgapi.lbl.gov/doc/restapi.html",
      "retrieved": "2026-09-22",
      "sha256": "d50ae0e269eb0dde19fea82099d0ea738c5b835bc1804068ad5b63537aa7b387",
      "units": 1
    },
    {
      "file": "pdg-listing.json",
      "role": "reference",
      "name": "PDG neutron mean-life listing",
      "url": "https://pdgapi.lbl.gov/listings/S017T",
      "licence": "CC BY 4.0",
      "licence_url": "https://pdgapi.lbl.gov/doc/restapi.html",
      "retrieved": "2026-09-22",
      "sha256": "348edc90c0616fe30e175e1d5a14aefe245c5a1c9ec3feec6e2e71195877daf0",
      "units": 30
    },
    {
      "file": "beta-relation.json",
      "role": "reference",
      "name": "Beta-decay relation, published bound conventions and claimant reply (factual transcription)",
      "url": "https://arxiv.org/pdf/1802.01804v3",
      "licence": "Factual transcription. Czarnecki et al. (PRL 120, 202002) and Dubbers et al. (PLB 791, 6-10) are published under CC BY 4.0 according to their Crossref records; the other cited works are linked and not redistributed.",
      "licence_url": "https://creativecommons.org/licenses/by/4.0/",
      "retrieved": "2026-09-22",
      "sha256": "0e553e99d52a0588b45fdf4044b1226e8baa5068effcc64d3cce1cf442d7e636",
      "units": 4
    },
    {
      "file": "pdg-lambda-summary.json",
      "role": "reference",
      "name": "PDG axial-coupling ratio summary",
      "url": "https://pdgapi.lbl.gov/summaries/S017AV",
      "licence": "CC BY 4.0",
      "licence_url": "https://pdgapi.lbl.gov/doc/restapi.html",
      "retrieved": "2026-09-22",
      "sha256": "c4341e1e4fea8f9fc69312fd4a048e3183b9f9085fea387bdf2056742382625f",
      "units": 1
    },
    {
      "file": "pdg-lambda-listing.json",
      "role": "reference",
      "name": "PDG axial-coupling ratio listing",
      "url": "https://pdgapi.lbl.gov/listings/S017AV",
      "licence": "CC BY 4.0",
      "licence_url": "https://pdgapi.lbl.gov/doc/restapi.html",
      "retrieved": "2026-09-22",
      "sha256": "40276b63bc5bb00b596b43f7e0a796978a020dba5fdbafcddede05ddd6027286",
      "units": 28
    }
  ],
  "anchor": {
    "what": "Numerical motivation for the theoretical proposal, from its published summary lifetimes.",
    "expected": "8.4 s; 4.0 σ; Br(n → p + anything) approximately 99%; dark branch approximately 1%",
    "computed": "8.4 s; 4.02287040 σ; Br(n → p + anything) 99.054054054%; dark branch 0.945945946%",
    "agrees": true,
    "tolerance": "Anchor tolerances: 0.05 s for the gap and 0.05 for significance, from rounding to one decimal. The approximate branch tolerance is 0.1 percentage points, a declared page convention rather than an experimental error. That convention alone cannot separate Equation (1) from treating the beam value as the total lifetime, which would give 0.955%, so the verifier also pins the branch to the exact fraction 7/740 within 1e-12."
  },
  "control": {
    "name": "UCNA pair-channel published-bound comparison under its signal and acceptance model",
    "citation": "X. Sun et al. (UCNA Collaboration, 2018), Search for dark matter decay of the free neutron from the UCNA experiment: n → χ + e+e−, Physical Review C 97, 052501(R). DOI: 10.1103/PhysRevC.97.052501. Numerical version: arXiv:1803.10890v1.",
    "computed": "0.945945946% / 0.01% = 94.594594595; constrained. Underlying experimental confidence limit not recomputed.",
    "as_printed": "Branch <10^-4 at >90% confidence for 100 keV < K_pair < 644 keV; ≫5σ for the experiment’s 1% dominant-pair hypothesis."
  },
  "power": {
    "grade": "B-published-sensitivity",
    "planted": "No observations planted. Reproduced claimed branch 0.945945946% set against UCNA’s published ceiling 0.01% under its signal and acceptance model.",
    "recovered": "No injection or recovery was run; published-bound comparison only.",
    "verdict": "By its own published sensitivity the control COULD have seen the claim in this channel: the reproduced dominant-pair prediction is 94.5946 times UCNA’s published ceiling, inside its open 100 to 644 keV window, under its signal and acceptance model. This trusts UCNA’s analysis; independent confirmation by injection was not tested. It says nothing about photon, invisible or other final states."
  },
  "null_through_claimant_method": {
    "applicable": false,
    "what": "Not applicable: this proposal interprets two published lifetime averages. It is not a selected peak whose search procedure can be run on comparable null records here. Equal lifetimes give a zero branch as an algebra check only; no false-positive rate is claimed.",
    "result": "Equal lifetimes give zero by algebra. No simulated null experiment or false-positive rate."
  },
  "verdict": {
    "category": "OPEN",
    "as_of": "2026-09-22",
    "sources": [
      "F. Takahashi et al. (Particle Data Group, 2026), Review of Particle Physics, International Journal of Modern Physics A 41, 2630011. Neutron mean-life listing S017T.",
      "X. Sun et al. (UCNA Collaboration, 2018), Search for dark matter decay of the free neutron from the UCNA experiment: n → χ + e+e−, Physical Review C 97, 052501(R). DOI: 10.1103/PhysRevC.97.052501. Numerical version: arXiv:1803.10890v1.",
      "Bartosz Fornal (2023), Neutron Dark Decay, Universe 9, 449. DOI: 10.3390/universe9100449. arXiv:2306.11349v1.",
      "Andrzej Czarnecki, William J. Marciano and Alberto Sirlin (2018), Neutron Lifetime and Axial Coupling Connection, Physical Review Letters 120, 202002. DOI: 10.1103/PhysRevLett.120.202002. Numerical version: arXiv:1802.01804v3.",
      "D. Dubbers, H. Saul, B. Märkisch, T. Soldner and H. Abele (2019), Exotic decay channels are not the cause of the neutron lifetime anomaly, Physics Letters B 791, 6-10. DOI: 10.1016/j.physletb.2019.02.013. arXiv:1812.00626v3.",
      "Y. Fuwa, T. Hasegawa, K. Hirota et al. (31 authors, 2024), Improved measurements of neutron lifetime with cold neutron beam at J-PARC. arXiv:2412.19519v1, submitted 27 December 2024.",
      "Ashish M. Desai (2026), Pressure-dependent detector effects in beam-based neutron lifetime measurements, The European Physical Journal A 62, 154. DOI: 10.1140/epja/s10050-026-01929-x.",
      "J. Caylor, R. Biswas, B. Crawford, M. S. Dewey, N. Fomin, G. L. Greene, S. F. Hoogerheide, J. Hungria-Negron, H. P. Mumm, J. S. Nico, F. E. Wietfeldt, D. O. Valete and J. Zuchegno (2025), Detection of molecular hydrogen in a neutron beam lifetime experiment, Physical Review C 112, 065501. DOI: 10.1103/nr3b-3dtl. arXiv:2506.01682v2.",
      "National Institute of Standards and Technology (2026), Spotlight: Electromagnetic Proton Trap at the NIST Center for Neutron Research (NCNR), news item dated 28 January 2026."
    ],
    "would_change": "An independently replicated non-proton decay, at a rate that accounts for the lifetime discrepancy, would support this explanation. A resolved measurement bias that removes the discrepancy would remove this motivation. A settled axial coupling would decide the beta-decay test: near aSPECT’s value the relation leaves room for the branch, and near PERKEO III’s it does not. Additional channel searches narrow particular models; agreement of lifetimes would not rule out every arbitrarily small exotic decay."
  },
  "decided_by": "not-yet",
  "years_to_decision": null,
  "choices": [
    {
      "id": "hypothesis",
      "label": "Pair hypothesis",
      "options": [
        "dominant",
        "companion",
        "custom"
      ],
      "default": "dominant",
      "affects": [
        "predicted pair branch",
        "ratio",
        "summary decision"
      ],
      "inert": false
    },
    {
      "id": "energy",
      "label": "Summed pair kinetic energy in keV",
      "options": [
        322,
        50
      ],
      "default": 322,
      "affects": [
        "applicability",
        "presence of numeric comparison"
      ],
      "inert": false
    },
    {
      "id": "share",
      "label": "Custom fraction of the proposed dark branch",
      "options": [
        1,
        0.1,
        0.01
      ],
      "range": {
        "engine_domain": [
          0,
          1
        ],
        "control": "logarithmic, any value between the presets",
        "control_log10_min": -4,
        "control_log10_max": 0,
        "control_log10_step": 0.01
      },
      "default": 1,
      "affects": [
        "predicted pair branch",
        "assigned seconds",
        "summary decision"
      ],
      "inert": false
    },
    {
      "id": "lifetimeCase",
      "label": "Second-layer lifetime sensitivity case",
      "options": [
        "central",
        "smaller",
        "larger"
      ],
      "default": "central",
      "affects": [
        "required branch",
        "pair share ceiling",
        "gap budget"
      ],
      "inert": false
    },
    {
      "id": "lambdaSource",
      "label": "Axial coupling in the beta-decay relation",
      "options": [
        "pdg2026",
        "favored2018",
        "perkeo3",
        "aspect"
      ],
      "default": "pdg2026",
      "affects": [
        "beta-decay clock",
        "implied exotic branch",
        "room for the whole required branch"
      ],
      "inert": false
    }
  ],
  "headline": "Read as a missing decay, the historical lifetime gap needs a 0.946% dark branch: UCNA constrains the searched pair channel, the beta-decay relation leaves room for the whole branch with only one of four axial-coupling values compared here (aSPECT’s), and the general explanation remains open.",
  "novelty": "we searched the Wasteland index, web results, arXiv-linked papers, GitHub search results and the Liu Lab lifetime-puzzle page on 2026-09-22 and did not find a public interactive page combining the original lifetime-branch calculation with UCNA's conservative pair-channel allocation ceiling and an explicit distinction between constrained and not decided by the published summary.",
  "ledger": {
    "claim_reproduced": {
      "value": true,
      "assertion": "anchor:historical-headline-and-corrupted-lifetime"
    },
    "control_computed": {
      "value": false,
      "assertion": "capability:published-summary-is-not-experimental-rerun"
    },
    "control_can_confirm": {
      "value": false,
      "assertion": "capability:grade-b-without-injection"
    },
    "rendered_figures_asserted": {
      "value": true,
      "assertion": "surface:every-static-figure-and-rendered-live-value"
    },
    "choices_are_live": {
      "value": true,
      "assertion": "choices:physical-cases-energy-share-corners"
    },
    "planted_fault_caught": {
      "value": true,
      "assertion": "fault:ceiling-times-one-hundred"
    },
    "refusal_asserted": {
      "value": true,
      "assertion": "refuse:scope-endpoints-units-kinematics-and-nonpositive-gap"
    },
    "provenance_pinned": {
      "value": true,
      "assertion": "provenance:all-frozen-bytes-sha256-and-research-copies"
    },
    "verdict_dated": {
      "value": true,
      "assertion": "verdict:open-date-primary-sources-and-change-evidence"
    }
  }
}