{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ff28590fd75edef8cceb14a0ed40ca97a4d18c16c423e32167d48961b8418461","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["40e47440a9ef804830289126ccb85e0b1efce18bd4227e7acbfac4e6bc714511","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"7da5a699cc419dc2f4a789fc606260ce5b0eee93d640e692010c83c34f84f19e","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":"2","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 $10^{-6}$ relative precision if a transverse polarization of about 5-10 percent builds up by the Sokolov-Ternov effect. For a $\\sim 9 \\times 10^{6}\\, \\mathrm{cm}$ 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 $\\sigma_E/E \\sim 4 \\times 10^{-4} \\text{ to } 10^{-3}$ and lattice errors, and whether calibration at the WW threshold is feasible.","problem_ref":"40e47440a9ef804830289126ccb85e0b1efce18bd4227e7acbfac4e6bc714511","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":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"e1bcfff2991524dfbe785ceea54ca732dad100cd8f0aa0c3d7d8e3c6668cea0e","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"60366810cb2dd144c5532a78e036b25137799ae2cd0457562608e41ea9b432e6","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"2bR1hvcBUzuZsyasVnIuQD2TxfdZpICcSfM0itCzEg9gkBOj95Zoykxg6j5cF_nDLYV5Cp0gRODgFRg4gEpIAg"},"schema":"pubphys.envelope/1"},"record_hash":"e1bcfff2991524dfbe785ceea54ca732dad100cd8f0aa0c3d7d8e3c6668cea0e","leaf_index":2510}