Electromagnetic Deflection Effects in the Integrated Luminosity Measurement at the CEPC

Abstract In order to ensure measurement of the integrated luminosity with a relative precision of $\mathrm{10^{-4}}$ at the $\mathrm{Z^{0}}$ pole at the Circular Electron Positron Collider (CEPC), numerous systematic effects have to be quantified and, if possible, corrected for. Here we discuss the collective impact of electromagnetic bunch fields on the initial-state electrons and positrons (EMD1) as well as on the Bhabha scattering final states (EMD2). Both effects change the four-momenta of the final-state particles, leading to modification of the Bhabha count in the luminometer. These effects are quantified in a simulation, together with their stability with respect to beam parameter variations. Possible correction methods based on experimental measurements with the CEPC detector are discussed on a conceptual level.