Scintillator Machining for the new Coordinate Detector in Jefferson Lab's High Momentum-Transfer Proton Electric Form Factor Experiment "GEp-5"

杰斐逊实验室高动量传输质子电形状因数实验“GEp-5”中新型坐标探测器的闪烁体加工

• 批准号: SAPEQ-2015-00015
• 负责人: Sarty, Adam
• 金额: $ 3.77万
• 依托单位: Saint Mary's University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Research Tools and Instruments
• 财政年份: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=591519
• 关键词: Scintillator; Machining; new; Coordinate; Detector

As part of the new experimental equipment required for use in conjunction with the just-completed 12 GeV energy upgrade at the Thomas Jefferson National Accelerator Facility ("Jefferson Lab") in Virginia, USA, the Super Bigbite Spectrometer ("SBS") detector facility is being developed/constructed in experimental Hall A. The SBS facility is being prepared primarily for use in a series of experiments dedicated to precision extraction of nucleon form-factors in high-energy elastic electron scattering. In particular, one of these SBS experiments will extend measurements of the proton’s electric form-factor to the highest values of momentum-transfer ever achieved - which effectively probes the distribution of electric charge inside the proton to the very smallest separation distances ever probed. To make this measurement, high-energy electrons (11 GeV) will elastically scatter from protons in a liquid hydrogen target, with recoiling protons being detected in the "SBS" itself - outfitted to also measure the polarization direction of the recoil protons - and the scattered electrons being detected in an electromagnetic calorimeter. The experiment will run at very high luminosity, and thus create a very high background radiation environment. In order to facilitate identification of the desired elastic-scattering reactions in this high-background situation, a Coordinate Detector ("CDet") is needed between the target and the electron calorimeter for a more precise measurement of the vertical scattering angle (compared to what will be possible with the calorimeter itself). This vertical coordinate detection will allow for selection of co-planar electron-proton final states when combined with the angle/position information of the proton detected in the SBS. This off-line co-planarity requirement is necessary to isolate and separate the desired elastic events from the high-level background. The Saint Mary’s group has worked with JLab staff for the past 5 years to assist in the development of a new, improved design for the CDet based on using two planes of vertically-stacked, thin (5 mm) scintillating bars (4 cm thick) to cover the needed area (294 cm x 104 cm) - requiring 2352 scintillating bars (each measuring 5 mm x 4 cm x 52 cm). The new design was presented to the SBS program’s Department of Energy review committee in Nov. 2013, and formally approved as part of the SBS Program Management Plan in April 2014 after undergoing a internal JLab technical review. The design relies on accurate alignment of each vertical stack of 588 bars to have a slight progressive tilt to allow the front face of each bar to remain perpendicular to a line extending from target centre; this alignment requirement will be achieved by precision machining along the 52cm length (top and bottom) of each bar. The resources from this equipment proposal will allow for this machining to be undertaken and accomplished.

作为与美国弗吉尼亚州托马斯杰斐逊国家加速器设施（“杰斐逊实验室”）刚刚完成的12 GeV能量升级结合使用所需的新实验设备的一部分，正在实验厅A开发/建造超级大比特分光计（“SBS”）探测器设施。 SBS设施的准备工作主要是为了在一系列实验中使用，这些实验致力于精确提取高能弹性电子散射中的核子形状因子。特别是，其中一个SBS实验将质子的电形状因子的测量扩展到有史以来实现的最高动量转移值-这有效地探测了质子内部的电荷分布到有史以来探测到的最小分离距离。为了进行这种测量，高能电子（11 GeV）将从液氢靶中的质子弹性散射，反冲质子在“SBS”本身中被检测到-配备也可以测量反冲质子的偏振方向-散射电子在电磁量热计中被检测到。实验将在非常高的光度下运行，从而创造一个非常高的背景辐射环境。为了便于在这种高背景情况下识别所需的弹性散射反应，在目标和电子量热计之间需要一个坐标检测器（“CDet”），以更精确地测量垂直散射角（与量热计本身相比）。当与SBS中检测到的质子的角度/位置信息结合时，该垂直坐标检测将允许选择共面电子-质子最终状态。这种离线共面性要求对于从高水平背景中隔离和分离期望的弹性事件是必要的。 圣玛丽团队在过去5年中与JLab工作人员合作，协助开发了一种新的改进型CDet设计，该设计基于使用两个垂直堆叠的薄（5 mm）隔离条（4 cm厚）平面来覆盖所需区域（294 cm x 104 cm）-需要2352个隔离条（每个尺寸为5 mm x 4 cm x 52 cm）。 新设计于2013年11月提交给SBS计划的能源部审查委员会，并在经过内部JLab技术审查后于2014年4月正式批准为SBS计划管理计划的一部分。 该设计依赖于588个棒的每个垂直堆叠的精确对准，以具有轻微的渐进倾斜，以允许每个棒的正面保持垂直于从目标中心延伸的线;该对准要求将通过沿着每个棒的52 cm长度（顶部和底部）的精密加工来实现。 本设备提案中的资源将允许进行并完成该加工。