Precision Polarimetry at the ILC: Concepts, Simulations and experiments

TL;DR

This paper discusses the development and testing of high-precision polarimeters for the ILC, including simulations, prototype design, and calibration efforts to achieve unprecedented measurement accuracy of beam polarization.

Contribution

It introduces a novel high-precision spectrometer prototype and comprehensive calibration methods to improve polarization measurement accuracy at the ILC.

Findings

Spin tracking simulations quantify polarization variation due to ground motion.

A prototype spectrometer for Compton polarimetry has been developed.

Calibration tests of photodetectors ensure measurement linearity.

Abstract

The precision physics program of the ILC requires precise knowledge of the state of beam polarisation. In fact the Compton polarimeters intended for the ILC will have to measure the polarisation with error a factor of 2 smaller than the previous best measurement at the SLAC SLD experiment. In order to further reduce measurement error, spin tracking simulations in the ILC Beam Delivery System subject to ground motion induced misalignment have been performed and the expected variation in polarisation has been quantified. A prototype of a high precision spectrometer to record Compton scattered electrons from the interaction of a longitudinal laser and the charged beams has been developed. The Compton electrons interact with a gas in the polarimeter channels to produce Cherenkov radiation measured by photodetectors. The calibration of the photodetectors is crucial and exhaustive bench tests of the photodetector linearity have been performed. The polarimeter prototype itself will be tested at the ELSA testbeam in Bonn in Spring 2009.