Polarimeter for High Energy Photons

自Thomas Jefferson国家实验室（JLAB）的连续电子束加速器设施建成以来，高能光子偏振的精确测量已成为一个重要的课题。例如，JLAB B厅的科学计划包括要求偏振测量精度至少达到5%的基本实验，其中一些要求精度为1-2%。计划中的D厅的物理项目也将在很大程度上依赖于必须精确了解其偏振的线性偏振光子。尽管有40多年的发展历史，高能光子偏振法仍然是一个相对不发达的领域。对于高能光子，如JLAB产生的那些，所有已知的测量偏振的方法都具有较低的分析能力，并且绝对精度低于批准和预期的物理程序所要求的。在这个项目中提出的偏振计在能量范围从几十mev到几个GeV的范围内，将具有无与伦比的实验不对称性约为1.7。该偏振光计结构简单，结构紧凑，其成本将低于根据任何其他可用方法建造的偏振光计。目前已经制造并测试了两个原型机。探测器和电子设备的性能达到了预期，测量的分析能力与预测的一样大。在spring -8上使用该偏振计，可以首次直接测量能量范围为1.5至2.4 GeV的线偏振光子产生的方位不对称对。然而，要制造出永久在JLAB使用的偏振计，还需要更多的改进。该项目将承担这些改进，包括对生产理论和计算的额外工作，数据采集和分析软件，以及探测器硬件的开发。除了解决偏振学的迫切需求，为JLAB的终极实验提供基础外，该计划的发展将为中央大学带来新颖的设备，并增加学生对研究的参与，促进来自弱势群体的本科生教育。

Since the completion of the Continuous Electron Beam Accelerator Facilityat Thomas Jefferson National Laboratory (JLAB), the precise measurement ofthe polarization of high energy photons has become an important topic.For example, the scientific program at JLAB's Hall B includes fundamentalexperiments that require polarization measurements to be accurate to atleast 5%, and some of them require an accuracy of 1-2%. The physicsprogram at the planned Hall D will also depend largely on linearlypolarized photons whose polarization must be accurately known. In spite of a history extending over 40 years, high energy photonpolarimetry is still a relatively undeveloped field. For high energyphotons, such as those produced at JLAB, all known methods for measuringpolarization have low analyzing power, and absolute accuracy below thatrequired for the approved and anticipated physics programs. Thepolarimeter proposed in this project will have an unsurpassed experimentalasymmetry of approximately 1.7 for an energy range from a few tens of MeVup to several GeV. The polarimeter is simple in construction, compact, andits costs will be lower than that for polarimeters built according to anyother available method. Two prototypes have already been built and tested. The performanceof the detectors and the electronics met expectations and the measuredanalyzing power was as large as predicted. The use of this polarimeter atSpring-8 enabled the first direct measurement of the azimuthal asymmetryin pair production by linear polarized photons in the energy range 1.5 to2.4 GeV. However, more improvements are needed to produce a polarimeterthat will be permanently in use at JLAB. This project will undertakethose improvements, including additional work on pair production theoryand calculations, data acquisition and analyzing software, and thedevelopment of detector hardware.In addition to solving urgent needs in polarimetry, providing the groundfor the ultimate experiments at JLAB, the development of this program willbring novel equipment to NCCU, and increase involvement of students inresearch, advancing the education of undergraduates from underrepresentedgroups.