{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b2e60c411e3e050c340636139e2cb3b4f7116dd0fe4e58b83a0cacb412646d51","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["84ce1c7bc46a6b9febd203bba7fde4af888b1a1871f94c4879fdfe4060d3970b","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"dd121813de63e3f62db282bea91ef60e9321d8a171fdf732eab780e5281c0814","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"nuc.precision-anomalies.x17-anomaly-origin","kind":"phenomenon","literature_status":"contested","n":"2","parents":[],"plain":"A group in Hungary (ATOMKI) saw too many electron-positron pairs emitted at large angles from excited beryllium, helium and carbon nuclei, as if a new particle of about 17 MeV were produced. Other experiments have not confirmed it.","posed_since":"2016","precise":"ATOMKI reported excesses in the e+ e- opening-angle distribution from internal pair creation in the 18.15 MeV 8Be (2016), 20.21 MeV 4He and 17.23 MeV 12C transitions, each consistent with a boson of mass about 16.7 to 17.0 MeV. Determine the origin: a new boson (X17), a standard nuclear-physics effect, or an instrumental artifact. Answer: the identified origin with independent experimental confirmation.","problem_ref":"84ce1c7bc46a6b9febd203bba7fde4af888b1a1871f94c4879fdfe4060d3970b","references":"","settled_by":"Independent repetition of the 8Be and 4He pair-emission measurements with different detectors, combined with direct searches for a 17 MeV boson coupled to electrons.","status_note":"MEG II (2024) found no signal in $7\\mathrm{Li}(p, e+ e-)8\\mathrm{Be}$ and set 90 percent CL limits $R < 1.8 \\times 10^{-6}$ ($17.6\\,\\mathrm{MeV}$) and $R < 1.2 \\times 10^{-5}$ ($18.1\\,\\mathrm{MeV}$) on the X17 branching ratio relative to gamma emission, while PADME (2025) reported an excess near $16.90\\,\\mathrm{MeV}$ with a global significance of about 2 standard deviations.","title":"Origin of the ATOMKI 17 MeV pair-emission anomaly","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"c88e47e949db3662e82d801e83482f62f036fda11dc7ede1d009664c218794a2","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"37383f405b602cd17c2224e4e515f109c3cddd91702eed82f61057226cc1cd48","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"D7bZKGDGge58Fwl5qC2MhmZPBAUnuVvbbsO1iMEFVqykzV5pPweKf0KjbmqqVRzfowschKghLLH4xACroEK0CQ"},"schema":"pubphys.envelope/1"},"record_hash":"c88e47e949db3662e82d801e83482f62f036fda11dc7ede1d009664c218794a2","leaf_index":3516}