{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"7470a716a8083531e3f7d2711b0ac127ab9af173e26a4363c89b3e5a30f1a6b9","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["33185324bb2c8ecbc05f6ecebae2d8261b242b9d27a25491c22e90093046363c","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"aec8706aa18e7da46cab3ac3d971980c6b48107fcf4acf63380dcf120a0f089e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"hep.flavor-anomalies.cabibbo-anomaly","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"The probabilities for an up quark to turn into each kind of down-type quark should add to exactly one. Current data fall short by about a tenth of a percent, roughly 3 standard deviations.","posed_since":"2018","precise":"Test $\\left|V_{ud}\\right|^2 + \\left|V_{us}\\right|^2 + \\left|V_{ub}\\right|^2 = 1$, with $V_{ud}$ from superallowed $0+$ to $0+$ nuclear beta decays and neutron decay, and $V_{us}$ from K_l3, K_mu2/pi_mu2 and $\\tau$ decays. The current deficit is of order $10^{-3}$ at about $3\\sigma$, together with an internal K_l3 versus K_mu2 tension; an answer is confirmation above $5\\sigma$ or resolution to below $2\\sigma$.","problem_ref":"33185324bb2c8ecbc05f6ecebae2d8261b242b9d27a25491c22e90093046363c","references":"","settled_by":"Improved electroweak radiative corrections and nuclear-structure corrections for superallowed decays, new lattice QCD form factors for K_l3, and new K_l3/K_mu2 ratio measurements (NA62).","status_note":"A 2026 lattice-QCD analysis (arXiv:2604.04715) and related work still find a first-row deficit near $3\\sigma$.","title":"Is first-row CKM unitarity violated (Cabibbo angle anomaly)?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"b1d2395e9738730d0516832b3ac0a2d99484ad3b84b28076e433d5bca3f4f6d4","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"3bde95352c69fce03eab8dea757631931cefb15dba95996c34930afd310a56d2","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"kArRm6qCjntxIPggOlwQxST_9zOSlQmNHu-ROYP4rT4w_IhmShAEcqquX_Ly2LTITO5bN0-jtUrt0Oz-0owoAA"},"schema":"pubphys.envelope/1"},"record_hash":"b1d2395e9738730d0516832b3ac0a2d99484ad3b84b28076e433d5bca3f4f6d4","leaf_index":3336}