{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"d7b25bfd8c0ed6d62084e576999c3b3d11c3da6689e94e00c087708cbc5b1751","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["41c19eed84fa3cbb2061dba471aada01e22074a80a41760fba17798f9c749435","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"354ac34a6ba5828c123597bfc1322d75f48d9eb72c9c47ef554f10f7010887fd","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.beam-beam-limit.crab-waist-instability","kind":"phenomenon","literature_status":"open","n":"2","parents":[],"plain":"New colliders cross very flat beams at a large angle with a special focusing scheme, the crab waist, to reach high collision rates. Unexpected instabilities, some involving the beam's interaction with its surroundings, have kept performance below design.","posed_since":"","precise":"In crab-waist schemes with Piwinski angle $\\phi >> 1$, strong-strong simulations predict coherent X-Z instabilities and interplay with longitudinal and transverse impedance. Determine the stability boundary in $(\\xi_x,\\xi_y,\\nu_s,\\mathrm{impedance})$ and whether it explains the luminosity shortfall of SuperKEKB relative to its design value of $8 \\times 10^{35}\\ \\mathrm{cm}^{-2}\\ \\mathrm{s}^{-1}$ (later target about $6.5 \\times 10^{35}$).","problem_ref":"41c19eed84fa3cbb2061dba471aada01e22074a80a41760fba17798f9c749435","references":"","settled_by":"Strong-strong simulations including impedance that reproduce measured SuperKEKB blow-up and luminosity, and machine experiments that confirm the predicted cures.","status_note":"SuperKEKB set a world-record peak of about $5.1 \\times 10^{34}\\,\\mathrm{cm}^{-2}\\,\\mathrm{s}^{-1}$ in December 2024, roughly 6 to 8 percent of its design and later target values; vertical blow-up, a vertical instability linked to collimator impedance and sudden beam losses are the identified limits.","title":"Beam-beam instabilities in large Piwinski angle crab-waist collisions","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"b18c04ab7f386f1198682f4bea2b64874d3572326a885fe51decbaa7657013cc","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"3ecfc18fa2136631831163fd827f1d2bb730e1e7b456ae720c5e44643abd58b4","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"jaJTwogssqgCW_ewNhqAvyr-6dgSsND6F1r-Nl7c5pJmgAyeuS1HMFSyMJ6iiqhQQf8ZfftePY0l65JluCCVCg"},"schema":"pubphys.envelope/1"},"record_hash":"b18c04ab7f386f1198682f4bea2b64874d3572326a885fe51decbaa7657013cc","leaf_index":2452}