{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"067bb538b50934d40007e6029ac3543074c2737c292cb2cba1afd8afe1b727c3","created":"2026-10-03T07:18:05Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","803f6c61383951a1e03e0a6e06849793a7e488ac6cf7c0b6df95233710df0a6b"],"salt":"20e2d988ecfd7fca65a8ae0376f5d033ac71009911ae324b1ecc4dbe4d302d00","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"hep.neutrino-mass.majorana-or-dirac","kind":"well-posed","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"803f6c61383951a1e03e0a6e06849793a7e488ac6cf7c0b6df95233710df0a6b","relation":"special_case"}],"plain":"If a neutrino is its own antiparticle, certain nuclei could undergo a double beta decay that emits no neutrinos at all. Its observation would show that lepton number is not conserved.","posed_since":"1937","precise":"Determine whether lepton number is violated by Majorana neutrino masses via neutrinoless double beta decay, with half-life T_1/2 ~ 1e26 to 1e28 yr for $m_{bb} \\sim 10\\ \\text{to}\\ 50\\ \\mathrm{meV}$. KamLAND-Zen (2024) gives T_1/2(Xe-136) > 3.8e26 yr, $m_{bb} < \\sim 28\\ \\text{to}\\ 122\\ \\mathrm{meV}$ (spread from nuclear matrix elements).","problem_ref":null,"references":"","settled_by":"Ton-scale double beta decay experiments (LEGEND-1000, nEXO, CUPID, KamLAND2-Zen) covering the inverted-ordering band $m_{bb} \\sim 15\\text{ to }50\\,\\mathrm{meV}$.","status_note":"No signal through 2025; the inverted-ordering band is partly probed.","title":"Are neutrinos Majorana particles, their own 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