Upgraded photon calorimeter with integrating readout for the Hall A Compton polarimeter at Jefferson Lab

Abstract

The photon arm of the Compton polarimeter in Hall A of Jefferson Lab has been upgraded to allow for electron beam polarization measurements with better than 1% accuracy. The data acquisition system (DAQ) now includes an integrating mode, which eliminates several systematic uncertainties inherent in the original counting-DAQ setup. The photon calorimeter has been replaced with a Ce-doped Gd 2 SiO 5 crystal, which has a bright output and fast response, and works well for measurements using the new integrating method at electron beam energies from 1 to 6 GeV.

The lowQ2chicane and Compton polarimeter at the JLab EIC

“…The one which was used for the HAPPEX experiment is a digital integration. A gate is open corresponding to one helicity window and all the samples are summed digitally [3], this allows to compute the integrated asymmetry without use of any thresholds as shown in Fig. 10.…”

Parity violation in electron scattering

“…Signal integration was found to be a powerful technique for operating in this range [82]. No energy calibration of the individual photons is needed, and the average energy depends on the precisely known beam energy.…”

Simple modification of Compton polarimeter to redirect synchrotron radiation

“…2. The synchrotron radiation spectra in the Compton photon detector, modeled for conditions during two completed experiments, HAPPEX III [3] and PVDIS [4], are compared to the spectrum obtained from modeling the 1. fixed periods of time [5], which avoid significant systematic uncertainties in calibrating the effects of a trigger threshold, require well-understood detector response even to low energies in the Compton spectrum. While the Compton spectrum is boosted to higher energy with higher beam energy (up to a few GeV for 11 GeV beam operation, compared to 600 MeV for 6 GeV beam), the energy endpoint and intensity of the SR spectrum rises more quickly.…”