Determination of electron beam polarization using electron detector in Compton polarimeter with less than 1% statistical and systematic uncertainty

Abstract

Title of Study: Determination of electron beam polarization using electron detector inCompton polarimeter with less than 1% statistical and systematic uncertainty Pages of Study: 250Candidate for Degree of Doctor of PhilosophyThe Q-weak experiment aims to measure the weak charge of proton with a precision of 4.2%. The proposed precision on weak charge required a 2.5% measurement of the parity violating asymmetry in elastic electron -proton scattering. Polarimetry was the largest experimental contribution to this uncertainty and a new Compton polarimeter was installed in Hall C at Jefferson Lab to make the goal achievable.In this polarimeter the electron beam collides with green laser light in a low gain FabryPerot Cavity; the scattered electrons are detected in 4 planes of a novel diamond micro strip detector while the back scattered photons are detected in lead tungstate crystals. This diamond micro-strip detector is the first such device to be used as a tracking detector in a nuclear and particle physics experiment. The diamond detectors are read out using custom built electronic modules that include a preamplifier, a pulse shaping amplifier and a discriminator for each detector micro-strip. We use field programmable gate array based general purpose logic modules for event selection and histogramming. Extensive Monte Carlo simulations and data acquisition simulations were performed to estimate the systematic uncertainties. Additionally, the Moller and Compton polarimeters were cross calibrated at low electron beam currents using a series of interleaved measurements. In this dissertation, we describe all the subsystems of the Compton polarimeter with emphasis on the electron detector. We focus on the FPGA based data acquisition system built by the author and the data analysis methods implemented by the author. The simulations of the data acquisition and the polarimeter that helped rigorously establish the systematic uncertainties of the polarimeter are also elaborated, resulting in the first sub 1% measurement of low energy (∼1 GeV) electron beam polarization with a Compton electron detector. We have demonstrated that diamond based micro-strip detectors can be used for tracking in a high radiation environment and it has enabled us to achieve the desired precision in the measurement of the electron beam polarization which in turn has allowed the most precise determination of the weak charge of the proton.

A novel comparison of Møller and Compton electron-beam polarimeters

“…A full Monte Carlo simulation of the Compton polarimeter using the GEANT3 [18] detector simulation package was used to validate the analysis procedure and to study a variety of sources of systematic uncertainties [10]. The list of contributions is shown in Table 2.…”

The low Q 2 chicane and Compton polarimeter at JLEIC

“…Beam polarization was measured for the QWeak experiment at 0.6 % accuracy [4] at electron energy of 1 GeV.…”

Precision Electron-Beam Polarimetry at 1 GeV Using Diamond Microstrip Detectors

“…1, and details can be found in Ref. [2,5]. The CW electron beam was deflected vertically by two dipole magnets to where it could interact with the photon target.…”

“…In order to meet the high-precision requirement of the Q weak experiment, a new polarimeter based on electronphoton scattering (Compton scattering) was constructed in experimental Hall C [2,5]. This polarimeter could be operated without disrupting the electron beam, allowing for continuous polarization measurement during the Q weak experiment.…”