{
  "kind": "attributed-context-facts",
  "as_of": "2026-09-22",
  "tang": {
    "citation": "Z. Tang et al. (2018), Search for the Neutron Decay n→X+γ, Where X is a Dark Matter Particle, Physical Review Letters 121, 022505. DOI: 10.1103/PhysRevLett.121.022505.",
    "url": "https://link.aps.org/accepted/10.1103/PhysRevLett.121.022505",
    "version": "APS accepted manuscript",
    "locations": "Physical PDF pages 7 and 8",
    "confidence": 0.97,
    "reference_branch": 0.013,
    "historical_photon_window_MeV": [
      0.782,
      1.664
    ]
  },
  "perkeo": {
    "citation": "M. Klopf, E. Jericha, B. Märkisch, H. Saul, T. Soldner and H. Abele (2019), Constraints on the Dark Matter Interpretation n → χ + e+e− of the Neutron Decay Anomaly with the PERKEO II experiment, Physical Review Letters 122, 222503. DOI: 10.1103/PhysRevLett.122.222503. arXiv:1905.01912v2.",
    "url": "https://arxiv.org/abs/1905.01912v2",
    "locations": "Abstract; physical PDF pages 3 and 4 (exclusion ranges)",
    "excluded_reference_branch": 0.01,
    "mass_coverage": 0.95,
    "own_lower_keV_90cl": 32,
    "own_lower_keV_5sigma": 37.5,
    "own_upper_keV_as_printed": 664,
    "observable": "summed-pair-kinetic-energy",
    "note": "The paper prints the upper end of both exclusion ranges as 664 keV; its own kinematic statement and UCNA give 644 keV. Only the lower thresholds are used on the page.",
    "review_kinetic_threshold_keV": 30,
    "threshold_source": "review2023"
  },
  "claim_scope": {
    "source": "claim",
    "photon_lead": "Conclusions, physical PDF page 5: monochromatic photons are \"the most striking signature\"; the simplest model predicts a photon channel at approximately 1%",
    "invisible_final_state_allowed": true,
    "invisible_location": "Physical PDF page 1, scenario (b) n to invisible; physical PDF pages 2 and 3, n to chi phi",
    "photon_unexplored_below_MeV": 0.782,
    "photon_unexplored_location": "Note added, physical PDF page 5: the case E_gamma < 0.782 MeV remains unexplored"
  },
  "review2020": {
    "citation": "Bartosz Fornal and Benjamín Grinstein (2020), Neutron's Dark Secret, Modern Physics Letters A 35, 2030019. DOI: 10.1142/S0217732320300190. arXiv:2007.13931v1.",
    "url": "https://arxiv.org/abs/2007.13931v1",
    "locations": "Sections 4.1 and 4.2, page 10; section 4.4 (proton-counting NIST and electron-counting J-PARC beam experiments called complementary), page 13",
    "photon_unconstrained_branch_max": 0.001,
    "photon_unconstrained_location": "Section 4.1, printed page 10: branching fractions up to about 0.1% are not constrained by the Los Alamos data for any dark matter mass"
  },
  "neutron_stars": {
    "source": "review2023",
    "max_mass_minimal_models_solar": 0.8,
    "observed_solar": 2,
    "remedy": "repulsive dark-sector self-interactions, or repulsion between the dark particle and the neutron",
    "locations": "Fornal 2023, section 5, printed page 17; the original Note added (physical PDF page 5) already cites the self-interaction route"
  },
  "caylor2025": {
    "citation": "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.",
    "url": "https://arxiv.org/abs/2506.01682v2",
    "locations": "Abstract (arXiv record and Crossref, published 12 December 2025)",
    "quote": "unlikely to have been significantly affected"
  },
  "nist2026": {
    "citation": "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.",
    "url": "https://www.nist.gov/news-events/news/2026/01/spotlight-electromagnetic-proton-trap-nist-center-neutron-research-ncnr",
    "date": "2026-01-28",
    "date_text": "28 January 2026",
    "quote": "We still don’t know the reason why the discrepancy exists."
  },
  "review2023": {
    "citation": "Bartosz Fornal (2023), Neutron Dark Decay, Universe 9, 449. DOI: 10.3390/universe9100449. arXiv:2306.11349v1.",
    "url": "https://arxiv.org/abs/2306.11349v1",
    "locations": "Sections 3 and 4; direct searches on page 12; beam and bottle experiments, page 15 (initial J-PARC data not yet precise enough to favour either result)"
  },
  "jparc": {
    "citation": "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.",
    "url": "https://arxiv.org/abs/2412.19519v1",
    "version": "arXiv:2412.19519v1; no journal reference on its arXiv record when checked",
    "locations": "Abstract",
    "detects": "beta-decay electrons, not protons",
    "lifetime_s": 877.2,
    "stat_s": 1.7,
    "sys_plus_s": 4.0,
    "sys_minus_s": 3.6,
    "tension_sigma_with_proton_beam_average": 2.3,
    "in_frozen_pdg_2026_listing": false
  },
  "desai": {
    "citation": "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.",
    "url": "https://doi.org/10.1140/epja/s10050-026-01929-x",
    "locations": "Publisher abstract only; no full-analysis verification claimed",
    "corrected_lifetime_in_abstract": false
  },
  "erratum": {
    "citation": "Bartosz Fornal and Benjamín Grinstein (2020), Erratum: Dark Matter Interpretation of the Neutron Decay Anomaly, Physical Review Letters 124, 219901(E). DOI: 10.1103/PhysRevLett.124.219901.",
    "url": "https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.219901",
    "locations": "Complete one-page erratum",
    "affected_original_equations": [
      5,
      6,
      7,
      15
    ]
  },
  "current_theory": {
    "citation": "M. Vikiaris, V. Petousis, M. Veselsky and Ch. C. Moustakidis (2026), Neutron dark decay and exotic compact objects, Physical Review D 114, 043032. DOI: 10.1103/21p6-sqfh.",
    "url": "https://journals.aps.org/prd/abstract/10.1103/21p6-sqfh",
    "locations": "Publisher abstract only; no full-analysis verification claimed"
  },
  "pdg": {
    "citation": "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.",
    "url": "https://pdgapi.lbl.gov/listings/S017T"
  },
  "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"
}