Electromagnetic deflection effects in the integrated luminosity measurement at the CEPC

TL;DR

This paper investigates electromagnetic deflection effects on Bhabha scattering measurements at CEPC, quantifies their impact through simulations, and discusses potential correction methods to achieve high-precision luminosity measurements.

Contribution

It provides a detailed simulation-based analysis of electromagnetic deflection effects and explores correction strategies for precise luminosity measurement at CEPC.

Findings

Electromagnetic fields cause measurable deflections affecting Bhabha counts.

Simulation shows the stability of these effects under beam parameter variations.

Conceptual correction methods are proposed for experimental implementation.

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 CEPC, numerous systematic effects have to be quantified and, if possible, corrected for. Here we discuss the impact of electromagnetic fields of incoming bunches on the initial state electrons and positrons (EMD1) as well as on the Bhabha scattering final states (EMD2). Both effects change four-momenta of the final state particles, leading to a modification of the Bhabha count in the luminometer. These effects are quantified in simulation, together with their stability with respect to the beam parameters variations. Possible correction methods based on experimental measurements with the CEPC detector are discussed on a conceptual level.