A Calibration System for Compton Polarimetry at $e^+e^-$ Linear Colliders

TL;DR

This paper presents a calibration system for Compton polarimeters at future electron-positron colliders, aiming to reduce systematic uncertainties to improve polarization measurement precision.

Contribution

It introduces an LED-based calibration method to monitor detector nonlinearities at the permille level, enhancing measurement accuracy.

Findings

Calibration system achieves <0.1% uncertainty in polarization measurement

Method effectively monitors detector nonlinearities at a few permille level

Implementation matches existing prototype detector performance

Abstract

Polarimetry with permille-level precision is essential for future electron-positron linear colliders. Compton polarimeters can reach negligible statistical uncertainties within seconds of measurement time. The dominating systematic uncertainties originate from the response and alignment of the detector which records the Compton scattered electrons. The robust baseline technology for the Compton polarimeters foreseen at future linear colliders is based on an array of gas Cherenkov detectors read out by photomultipliers. In this paper, we will present a calibration method which promises to monitor nonlinearities in the response of such a detector at the level of a few permille. This method has been implemented in an LED-based calibration system which matches the existing prototype detector. The performance of this calibration system is sufficient to control the corresponding contribution to the total uncertainty on the extracted polarisation to better than $0.1\%$.