{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f1cad6fb249d9a4f80851680be7de7de6bd53e856ffe2e6926e5a0b2fd92eaad","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"2e1a9be481dc6b8cd8b07fa6381ac8ad8c27e96518c22bb7d7a762160539c259","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"beams.polarized-beams.fccee-energy-calibration","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Measuring a collider's beam energy to a part per million uses spins that line up by themselves through synchrotron radiation; at higher energies this alignment is weak and easily destroyed.","posed_since":"","precise":"Resonant depolarization gives the beam energy to below 1e-6 relative precision if a transverse polarization of about 5-10 percent builds up by the Sokolov-Ternov effect. For a $\\sim 9e6\\, \\mathrm{cm}$ circumference ring at $E = 45.6\\, \\mathrm{GeV}$ and $E \\sim 80\\, \\mathrm{GeV}$, determine the equilibrium polarization and build-up time with polarization wigglers, including depolarization from energy spread $\\sigma_E/E \\sim 4e-4 \\text{ to } 1e-3$ and lattice errors, and whether calibration at the WW threshold is feasible.","problem_ref":null,"references":"","settled_by":"Spin-diffusion calculations with realistic errors and wiggler settings, validated against LEP polarization data.","status_note":"","title":"Self-polarization for energy calibration at FCC-ee Z and WW energies","topic_ref":"9b02c27128b03f7c327a7c52a19b27e591b0902b0604205d7218c8dbadece62a"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"40e47440a9ef804830289126ccb85e0b1efce18bd4227e7acbfac4e6bc714511","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"6eac8d09a26bb4c24a9a9e3bcb608ca949b4c65bd347f8e84f7c8d8ccae9f413","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"fKaJTv_uvAuRooeBpNkszdHnW-xG5ZLL_WSIDowUXj56GPFlr3o9t0RZtHLgMzNaKqU5MKwxc8SX-ILFRsLTBQ"},"schema":"pubphys.envelope/1"},"record_hash":"40e47440a9ef804830289126ccb85e0b1efce18bd4227e7acbfac4e6bc714511","leaf_index":687}