{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3d6c6fbdb32a19699e42f41a609cfe5b4e12222a11889954fdcb8240004e78d0","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["2525faffc272c86574c0ba515e8b1046c8750641804f8e7550dbf929c9641853","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"bfad5e52927e331faa75c2a281b94f35d44c2504fef311fed2f351955640c33f","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":["ai:gpt-5.5"],"external_id":"amo.fine-structure-constant.electron-g2-sm-test","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"The electron behaves like a tiny magnet whose strength has been measured to about one part in ten trillion. Using $\\alpha$ from atom experiments, theory predicts the same number, and any mismatch would point to new particles or forces.","posed_since":"","precise":"With $g/2 = -\\mu_e/\\mu_B$ measured to 0.13 ppt ($a_e = (g-2)/2$ to 0.11 ppb, absolute uncertainty $1.3 \\times 10^{-13}$; Fan et al 2023) and $a_e(\\mathrm{SM})$ computed from $\\alpha(\\mathrm{recoil})$ plus QED (five-loop coefficient now agreed between two groups), hadronic and electroweak terms, determine whether $\\delta a_e = a_e(\\exp) - a_e(\\mathrm{SM})$ differs from zero; at present $\\delta a_e$ has opposite signs for $\\alpha(\\mathrm{Cs})$ and $\\alpha(\\mathrm{Rb})$, at roughly $-2.2\\ \\sigma$ and $+2\\ \\sigma$. The answer is $\\delta a_e$ with total uncertainty below $10^{-13}$ and its significance.","problem_ref":"2525faffc272c86574c0ba515e8b1046c8750641804f8e7550dbf929c9641853","references":"","settled_by":"Resolution of the Cs-Rb $\\alpha$ discrepancy combined with an improved $a_{e}$ measurement, yielding a single $\\delta a_{e}$ with uncertainty below $10^{-13}$.","status_note":"The $5\\sigma$ disagreement between the two five-loop QED evaluations was removed in December 2024 (arXiv 2412.06473), so the remaining obstacle is the Cs-Rb $\\alpha$ discrepancy.","title":"Is the electron magnetic moment anomaly consistent with the Standard 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