{"paper":{"title":"Pion Beta Decay and CKM Unitarity","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"","cross_cats":["hep-ex","hep-lat","nucl-th"],"primary_cat":"hep-ph","authors_text":"Alberto Sirlin, Andrzej Czarnecki, William J. Marciano","submitted_at":"2019-11-12T05:42:45Z","abstract_excerpt":"Pion beta decay, $\\pi^+\\to \\pi^0 e^+\\nu(\\gamma)$, provides a theoretically clean $\\pm 0.3\\%$ determination of the CKM matrix element $V_{\\text{ud}}$. That value falls short of super-allowed nuclear beta decays where an order of magnitude better precision already exists. We advocate a new strategy for utilizing pion beta decay, based on its role in determining ${V_{\\text{us}} / V_{\\text{ud}}}$ via the ratio $R_V=\\Gamma\\left(K\\to \\pi l \\nu(\\gamma)\\right)/\\Gamma\\left(\\pi^+\\to \\pi^0 e^+\\nu(\\gamma)\\right)$. $R_V$ measures $ { f_+^K(0) |V_{\\text{us}}| / f_+^\\pi(0) |V_{\\text{ud}}| }$ and is insensiti"},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"1911.04685","kind":"arxiv","version":2},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/1911.04685/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}