Evaluation of radiative depolarization in the future Circular Electron-Positron Collider

Abstract

Polarized lepton beams are an important design aspect of the future 100 km-scale Circular Electron-Positron Collider (CEPC). Precision beam energy calibration using resonant depolarization, as well as longitudinally polarized colliding beams are being actively investigated. The achievable beam polarization level for different beam energies and application scenarios depend on the radiative depolarization in the collider rings. In this paper the radiative depolarization effects are evaluated for a the CEPC collider ring lattice with detailed machine imperfections and corrections. Simulations with the SLIM and Monte-Carlo approaches using the BMAD/PTC codes are compared with the theory of spin diffusion effects for ultra-high beam energies.

Investigation of spin rotators in CEPC at the Z-pole

“…Other kinds of machine imperfections also affect the orbital motion and the degree of equilibrium polarization; a systematic approach of error correction is under development [37]. Evaluation of the influence of these errors on the equilibrium polarization for a CEPC lattice without spin rotators is reported in [38], which shows a relatively high beam polarization is achievable at the Z-pole energy after the error correction. In future studies, we will introduce machine imperfections for the whole collider ring with spin rotators and evaluate the performance after a dedicated correction scheme.…”