{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b757db5d416f8b9cc8726503a790f50ca6964c2d8e52ae8e2e3abfbe6eeb99c0","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"aee53225cdc2c1e8c41f2b94c9685b638c73edfc7ba616743c2412dcdce3385a","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"beams.collective-instabilities.beam-beam-limit","kind":"well-posed","literature_status":"open","n":"1","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":null,"references":"","settled_by":"A theory or strong-strong simulation predicting xi_y,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":"dd60e631adb08b9b18495c7a3ab1cfd2ffd7375b33108ba5cf5ec6cce7af2868"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"c7f3731a615018b75f1e6a39418abb3757e0b3f549578cfb9b41d7d935a3c429","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"3c8a47347d31961e1b799e78f5bddc392e2c436a974ec07877e9e0c69459f23b","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"ODtCy52PlG9IwxPE-wZITxYPfhVScR-eQ3LZAYn4IvUO2TJl-Vy6CbNOa14l9iJgln4GTU3bhOW1OeyFk5InBw"},"schema":"pubphys.envelope/1"},"record_hash":"c7f3731a615018b75f1e6a39418abb3757e0b3f549578cfb9b41d7d935a3c429","leaf_index":654}