Precision Measurement of Electromagnetic Properties of Light Pseudoscalar Mesons via the Primakoff Effect

该项目旨在将对杰斐逊实验室正在进行的研究的重要贡献与为有前途的本科生提供的教育经验相结合。一个由本科生和一名全职教师组成的团队将在杰斐逊实验室和北卡罗来纳大学威尔明顿分校(UNW)探测器开发实验室开展这项工作。这个项目的主要目标是优化本科生的实验，同时通过高精度测量双光子衰变宽度和三个中性光伪标量介子的跃迁形状因子，从而为我们理解低能QCD做出重要贡献。QCD中的两个基本现象，即手征对称性的自发破缺和手征反常，在轻伪标量介子区以最明确的形式表现出来。这些反常现象特别地驱动了π介子的双光子衰变--零，ETA和ETA‘，并且还提供了ETA’的很大一部分质量。联合国教科文组织将致力于目前中性介子寿命实验的高精度测量，而杰斐逊实验室12GeV电子束的出现将使这一计划扩展到ETA和ETA。这些测量将对目前关于夸克质量比、ETA和ETA‘的混合角的知识产生重大影响，并提供对介子电磁相互作用半径大小的模型独立提取。此外，对赝标介子跃迁形式因子的更精确的了解将使我们能够更好地确定光散射对介子反常磁矩的贡献，这是超越标准模型的新物理最敏感的量之一。UNW小组将在开发多通道闪烁束轮廓探测器方面发挥主导作用，通过蒙特卡罗模拟优化实验装置，为未来的ETA和ETA的测量提供蒙特卡罗模拟，同时继续为中性介子寿命测量实验开发多通道晶体量能器和对谱计项目做出重大贡献。这项研究将邀请本科理科专业的学生作为主要贡献者。本科生的参与已经成为UNW研究小组的商标之一，并符合该大学提供高质量本科生学习体验的承诺

This project is designed to integrate important contributions to the ongoing research at Jefferson lab with an educational experience for promising undergraduate students. A team of undergraduate students and one full time faculty member will carry out this work both at Jefferson Lab and in the University of North Carolina at Wilmington (UNCW) detector development laboratory. The primary goal of this project is to optimize the undergraduate experience while making important contribution to our understanding of low energy QCD by carrying out the high precision measurements of two-photon decay widths and the transition form factors of three neutral light pseudoscalar mesons pion-zero, eta and eta' (eta-prime) via the Primakoff effect. Two basic phenomena in QCD, namely the spontaneous break of chiral symmetry and the chiral anomalies, are manifested in their most unambiguous form in the sector of light pseudoscalar mesons. The anomalies particularly drive the two-photon decays of the pion-zero, eta and eta' and also provide a large fraction of the eta' mass. The UNCW group will work on current development of a high precision measurement of neutral pion lifetime experiment, while the advent of a 12 GeV electron beam at Jefferson Laboratory will make it possible to extend this program to eta and eta'. These measurements would have a significant impact on the current knowledge of the ratios of quark masses, the mixing angle of eta and eta', and provide model independent extractions of the size of the electromagnetic interaction radii of mesons. In addition, more precise knowledge of the transition form factors of the pseudoscalar mesons will allow a better determination of the light-by-light scattering contributions to the anomalous magnetic moment of the muon, which is one of the most sensitive quantities to new physics beyond the Standard Model.The UNCW group will play a leading role in developing a multi-channel scintillating beam profile detector, optimizing the experimental setup for future eta and eta' measurements by Monte Carlo simulation, while continuing to make significant contributions to develop a multi-channel crystal calorimeter and pair-spectrometer projects for the neutral pion lifetime measurement experiment. This research will engage undergraduate science majors as key contributors. The involvement of undergraduates has become one of the trademarks of the UNCW research group and matches the university's commitment to provide a high quality undergraduate learning experience