{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"657b8e21749aab27f4d201c6e97c084fe6e209b0574088368bef7d46414741af","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["39a558bd6ce48b8496559b26e619658f7c31e51e5cea86820886b0ce62d747a6","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"e3b32db4b7555ca2ac9f317e5626e8438976e18ca125e7be869a46f40d277c9e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"hep.flavor-anomalies.b-k-nunu","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Belle II found that B mesons decay to a kaon plus invisible particles more often than expected, about four times the predicted rate. It could be new particles or a fluctuation.","posed_since":"2023","precise":"Belle II (2023) measured BR(B+ -> K+ nu nubar) = (2.3 +- 0.7) x $10^{-5}$, $2.7\\,\\sigma$ above the SM prediction ($\\sim 0.5 \\times 1e-5$). Determine whether the excess persists at $\\ge 5\\,\\sigma$ and whether it shows a peak in invisible mass from a new light particle.","problem_ref":"39a558bd6ce48b8496559b26e619658f7c31e51e5cea86820886b0ce62d747a6","references":"","settled_by":"Belle II with about 5 to 10 $\\mathrm{ab}^{-1}$ and NA62-style rare kaon decays for related b to s and s to d invisible channels.","status_note":"The $2.7\\sigma$ excess is still the latest measurement as of 2026.","title":"Is the Belle II $B\\,\\mathrm{to}\\,K\\,\\nu\\,\\nu$ excess 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