基于定标器的深度非弹性散射宇称非对称性测量系统
A Scaler-Based Data Acquisition System for Measuring Parity-Violating Asymmetry in Deep Inelastic Scattering
摘要：
测量深度非弹性散射中宇称破坏不对称性的实验在实验大厅A的托马斯·杰斐逊国家加速器设施完成。从这些不对称性中，可以提取夸克弱轴荷的组合，其精度比世界数据提高五倍。为了实现这一点，在$10^{-4}$水平的不对称性需要在事件率高达600 kHz和高π介子背景下进行测量典型的深度非弹性散射实验需要有效地拒绝。成功开发并使用了具有固有颗粒识别（PID）的专用数据采集（DAQ）系统：在实验的大部分生产期间，电子样品中的π介子污染被控制在$2\times 10^{-4}$或更低的数量级，电子效率高于91%，由于DAQ死时间而测量的不对称性的系统不确定性低于0.5%，并且不对称测量的统计质量与高斯分布一致超过五个数量级。重点介绍了数据采集系统的设计方案、实现的PID性能、死区效应和测量微小不对称性的能力。
英文摘要：
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.
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