A Scaler-Based Data Acquisition System for Measuring Parity-Violating Asymmetry in Deep Inelastic Scattering

TL;DR

This paper presents a specialized scaler-based data acquisition system developed for precise measurement of parity-violating asymmetries in deep inelastic scattering, achieving high efficiency, low background contamination, and improved accuracy over previous data.

Contribution

The paper introduces a novel DAQ system with intrinsic particle identification that effectively measures tiny asymmetries and controls background contamination in deep inelastic scattering experiments.

Findings

Achieved electron efficiency above 91% during most of the experiment

Controlled pion contamination to below 2×10^{-4}

Systematic uncertainty due to deadtime was under 0.5%

Abstract

An experiment that measured the parity-violating asymmetries in deep inelastic scattering was completed at the Thomas Jefferson National Accelerator Facility in experimental Hall A. From these asymmetries, a combination of the quark weak axial charge could be extracted with a factor of five improvement in precision over world data. To achieve this, asymmetries at the $10^{-4}$ level needed to be measured at event rates up to 600 kHz and the high pion background typical to deep inelastic scattering experiments needed to be rejected efficiently. A specialized data acquisition (DAQ) system with intrinsic particle identification (PID) was successfully developed and used: The pion contamination in the electron samples was controlled at the order of $2\times 10^{-4}$ or below with an electron efficiency of higher than 91 % during most of the production period of the experiment, the systematic uncertainty in the measured asymmetry due to DAQ deadtime was below 0.5 %, and the statistical quality of the asymmetry measurement agreed with the Gaussian distribution to over five orders of magnitudes. The DAQ system is presented here with an emphasis on its design scheme, the achieved PID performance, deadtime effect and the capability of measuring small asymmetries.