{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"324f461473eb656d25bc1d6679b4a3b17d816164422796435b18f7fba1fcbf9e","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["c7f3731a615018b75f1e6a39418abb3757e0b3f549578cfb9b41d7d935a3c429","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"f662c2972ea40893cb20d7044851dcdc2f4b0fbba94f31a0634c0a3169a8436b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":["ai:gpt-5.5"],"external_id":"beams.collective-instabilities.beam-beam-limit","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Colliding beams focus each other; above a certain strength they blow up, and that ceiling is known from experience rather than derived.","posed_since":"","precise":"In $e+e-$ ring colliders the vertical beam-beam parameter $\\xi_y$ has saturated in operation at approximately 0.03-0.09 (highest values at LEP and KEKB), with simulations suggesting higher limits at stronger damping; with crab-waist collisions and beamstrahlung, coherent X-Z instabilities intervene. Derive the maximal $\\xi_y$ as a function of radiation damping time per turn, synchrotron tune, Piwinski angle and beamstrahlung parameters, and compare with SuperKEKB, DAFNE and LEP data.","problem_ref":"c7f3731a615018b75f1e6a39418abb3757e0b3f549578cfb9b41d7d935a3c429","references":"","settled_by":"A theory or strong-strong simulation predicting $\\xi_y,\\mathrm{max}$ for the three colliders within 20 percent with one set of assumptions.","status_note":"","title":"What sets the beam-beam tune-shift limit in electron-positron colliders?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"b7a5903913c2edabf609143fbfdb7e1cfd3415bfeff8dca8e82c2472c6bc3c89","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"2b7b62dfa885acf88d07d035e236385f36cb60b47f45899ab049b873f80c7e42","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"1Va4_q6xT0BVYDtlurNkhZtQTbECNPzDWGS2EeUZ-filZXxauCfAuXtQEjh-169FDQXD1mAt9_iAzDHXivb-CA"},"schema":"pubphys.envelope/1"},"record_hash":"b7a5903913c2edabf609143fbfdb7e1cfd3415bfeff8dca8e82c2472c6bc3c89","leaf_index":2466}