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    "story_id": "mp-2026-10-20-002",
    "source_story_id": "tmp-feature-weak-magnetism-neutron",
    "edition_id": "mp-2026-10-20-morning-0102",
    "edition_url": "https://themachinepress.com/edition/2026-10-20",
    "position": 2,
    "story_type": "secondary",
    "section": "research",
    "editorial_classification": "editorial",
    "headline": "Weak Magnetism Appears in the Free Neutron",
    "slug": "weak-magnetism-appears-in-the-free-neutron",
    "dek": "Combining beta asymmetry, neutron lifetime and superallowed-decay measurements lifted a long-standing degeneracy and produced a 5.1-sigma signal.",
    "summary": "Combining beta asymmetry, neutron lifetime and superallowed-decay measurements lifted a long-standing degeneracy and produced a 5.1-sigma signal.",
    "body_text": "Nearly seven decades after Murray Gell-Mann introduced weak magnetism as a consequence of the conserved vector current hypothesis, researchers report its first observation in free-neutron decay. Beta asymmetry alone cannot separate the weak-magnetism form factor from the axial-to-vector coupling ratio, so the analysis combines asymmetry measurements with the neutron lifetime and the comparative half-life of superallowed nuclear decays. Current data yield a form factor of 4.47 with an uncertainty of 0.87, consistent with the predicted 4.71 and excluding no weak magnetism at 5.1 sigma. Across variations of the internally tense neutron dataset, the reported significance remains between 5.0 and 6.1 sigma. This is an inference from combined existing measurements, not a new detector event; its value is that three familiar observables expose a property each could not isolate alone.",
    "why_it_matters": "Combining beta asymmetry, neutron lifetime and superallowed-decay measurements lifted a long-standing degeneracy and produced a 5.1-sigma signal.",
    "limitations": [
      "Beta asymmetry alone cannot separate the weak-magnetism form factor from the axial-to-vector coupling ratio, so the analysis combines asymmetry measurements with the neutron lifetime and the comparative half-life of superallowed nuclear decays.",
      "This is an inference from combined existing measurements, not a new detector event; its value is that three familiar observables expose a property each could not isolate alone."
    ],
    "importance": 9,
    "canonical_url": "https://themachinepress.com/story/mp-2026-10-20-002/weak-magnetism-appears-in-the-free-neutron",
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    "first_published_at": "2026-10-20T09:00:00.000-04:00",
    "modified_at": "2026-10-20T09:00:00.000-04:00",
    "content_status": "new",
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        "text": "Combining beta asymmetry, neutron lifetime and superallowed-decay measurements lifted a long-standing degeneracy and produced a 5.1-sigma signal.",
        "source_ids": [
          "source-2026-10-20-002"
        ],
        "qualification": "Beta asymmetry alone cannot separate the weak-magnetism form factor from the axial-to-vector coupling ratio, so the analysis combines asymmetry measurements with the neutron lifetime and the comparative half-life of superallowed nuclear decays."
      }
    ],
    "source_ids": [
      "source-2026-10-20-002"
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    "tags": [
      "neutron decay",
      "weak magnetism",
      "particle physics",
      "conserved vector current"
    ],
    "image_url": "https://themachinepress.com/issues/2026-10-20/feature-weak-magnetism.png",
    "corrections": []
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  "sources": [
    {
      "source_id": "source-2026-10-20-002",
      "title": "arXiv preprint 2610.26792, original v1",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2610.26792v1",
      "canonical_url": "https://arxiv.org/abs/2610.26792v1",
      "source_type": "primary_research",
      "is_primary_source": true,
      "published_at": "2026-10-19T13:40:03.000-04:00",
      "accessed_at": "2026-10-20T08:15:06.176-04:00",
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  "publisher": {
    "name": "The Machine Press",
    "url": "https://themachinepress.com",
    "description": "A daily newspaper for the age of artificial intelligence."
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  "cite_this_report": {
    "title": "Weak Magnetism Appears in the Free Neutron",
    "publisher": "The Machine Press",
    "published_at": "2026-10-20T09:00:00.000-04:00",
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