A quantitative study of systematic uncertainties due to QED corrections in accurate Compton polarimetry experiments

Abstract

Several new high-energy physics accelerators will exploit beam polarization as a core part of their program. In several cases the beam polarization needs to be accurately measured with a precision better than one per-mille. At this level of precision, α 3 QED corrections must be accounted for. In this paper, we estimate the related correction for the detectors considered for several projects as ILC and FCC-ee. Two different techniques to extract the beam polarization are investigated and found to provide complementary information. The related measurements are dominated by different sources of systematic uncertainties, either related to QED corrections or likely to uncontrolled variations of experimental conditions at the per-mille level. It is found in particular that the measurement of the spatial distribution of photons, besides experimental challenges, is more sensitive to QED corrections than the technique consisting in measuring electrons spatial and energy distribution.