Evaluation of radiative depolarization in the future circular electron-positron collider

Spin-polarized lepton beams are an important aspect in the design 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, is being actively investigated. The attainable beam polarization level for various beam energies and application scenarios depends on the radiative depolarization in the collider rings. In this paper, the radiative depolarization effects are evaluated for a 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 the effects of spin diffusion for ultrahigh beam energies and the validity of the theories, with special attention to that of so-called uncorrelated resonance crossing, is thereby addressed.