Polarization issues in circular electron–positron super-colliders

Abstract

We study a possibility of obtaining transversely polarized electron/positron beams in the CEPC collider. Also, original results are presented for another project, the FCCee collider, which allows us to identify some features and differences of these similar machines. Important is the comparison of the data obtained with the expected and measured polarizations at LEP. In estimation of the depolarizing effect of field errors, in addition to the usual nonresonant spin diffusion, an attempt was made to take into account the resonant diffusion, which is due to a large spin tune spread. We consider a possibility to obtain polarization by accelerating polarized particles in the CEPC booster and then injecting them into the main ring. This option can be crucial for obtaining longitudinal polarization. We propose a scheme in which long-term preservation of such polarization is possible.

Investigation of spin rotators in CEPC at the Z-pole

“…The above simulations indeed confirm the analysis that depolarization effects could be largely suppressed in such an anti-symmetric structure in Refs. [15,16].…”

“…Koop also discussed this kind of spin rotators for the SuperB project [13,14] later. Nikitin first pointed out such a scheme could be modified and applied in the CEPC at the Z-pole energy [15,16], using the fact that the interaction region design features a S-shaped twisted orbit in the median plane, i.e., the spin rotators can be arranged in an "anti-symmetric" manner, which would cancel most of the depolarization effects due to quantum fluctuation [11]. Recently, a solenoid-based spin rotator has been designed for the electron longitudinal polarization in the electron-ion collider (EIC) [17].…”

A toy Monte Carlo simulation for the transverse polarization of high-energy electron beams

“…Besides, possibility to realize longitudinally polarized colliding beams is under study, one reasonable approach is to generate polarized electron beam from the source, and inject into the collider ring. To this end, spin rotators [32] are required in the collider ring while Siberian snakes [33] are needed in the booster to maintain the beam polarization during acceleration. As a concrete application example, we performed a toy Monte Carlo simulation to measure the transverse polarization of the high-energy electron beam for CEPC on the Z pole.…”

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

“…Mane worked out a scaling of equilibrium beam polarization at ultra-high beam energies and studied possibilities of using Siberian snakes to mitigate the depolarization while retaining self-polarization at the same time [23]. Nikitin theoretically evaluated the radiative depolarization and the equilibrium transverse polarization in these super electron-positron circular colliders, and discussed options to achieve longitudinal polarized colliding beams [24,25]. There are also attempts to re-evaluate the radiative depolarization and equilibrium beam polarization using the Bloch equation approach [26,27].…”