Precision Experiments to Study Fundamental Properties of Hadrons via Electromagnetic Probes at Jefferson Lab

在这个奖项的支持下，两个实验项目将在杰斐逊实验室进行，由PI和他的团队直接领导。第一个项目是早期实验的延伸，旨在测量强相互作用粒子（埃塔介子）衰变成两个光子的概率，光子是波长非常短的光粒子。介子的性质对基本对称性非常敏感，最重要的是，对这些对称性的自发和显式破坏非常敏感。对称破缺的影响在宇宙可见物质的形成中起着至关重要的作用。第二个项目是准备一个升级的实验，通过弹性散射质子的电子来重新测量质子的电荷半径。这个实验被称为PRad- ii，它的目标是确定质子的电荷半径，比第一次PRad实验精确四倍，PRad实验也是由PI领导的。北卡罗来纳农业技术州立大学的大多数学生是非裔美国人，PI将从这些学生中招募学生与他一起进行这些实验。该奖项将支持一名本科生，一名研究生和一名博士后，他们将接受高技术技能的指导和培训，为他们在STEM领域的职业生涯做好准备。在这个奖项的支持下，PI和他的团队将测量eta衰变到2个光子的概率，不确定性为3%。这种精度水平将通过将剩余的衰变通道修正为其他基本粒子，对粒子数据组（PDG）编译中的eta扇区产生重大影响。这将大大提高我们对轻夸克质量比的理解，这是一种直接的、与模型无关的方式。该奖项支持的第二个项目是在杰斐逊实验室准备一个新的、升级的实验来重新测量质子电荷半径（PRad-II）实验。PI的第一次实验（PRad）的结果与子氢光谱测量的小半径一致，并在最近修订CODATA推荐的质子半径中发挥了关键作用。在拨款期间，项目负责人和他的小组将开发、建造、测试和安装新的探测系统，将第一次实验的结果提高四倍。这将是电子-质子散射实验中对质子半径最精确的测量。有了这个精度，PRad- ii实验将解决PRad和其他电子-质子散射结果之间的电流差异。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support from this award two experimental projects will be conducted at Jefferson Laboratory under the direct leadership of the PI and his group. The first project is the extension of an earlier experiment to measure the probability of a strongly interacting particle (the eta meson) decaying into two photons, which are light particles with very short wavelengths. The properties of eta mesons are very sensitive to fundamental symmetries and, most importantly, the spontaneous and explicit breaking of those symmetries. The effects of symmetry breaking plays critical roles in the formation of the visible matter in Universe. The second project is the preparation of an upgraded experiment to re-measure the proton charge radius by elastically scattering electrons from protons. The experiment is called PRad-II, and its goal is to determine the proton’s charge radius four times more precisely than the first PRad experiment, which the PI also led. The majority of students at North Carolina Agricultural & Technical State University are African American, and the PI will recruit students from that pool to work with him on these experiments. This award will support one undergraduate student, one graduate student, and one postdoctoral fellow who will be mentored and trained in highly technical skills that will prepare them for careers in STEM fields. With support from this award the PI and his group will measure the probability of eta decay to 2 photons with an uncertainty of 3%. That level of precision will significantly impact the eta-sector in the Particle Data Group’s (PDG) compilation by correcting the remaining eta-decay channels to other elementary particles. This will significantly improve our understanding of the light quark mass ratio in a direct and mostly model independent way. The second project supported by this award is the preparation of a new, upgraded experiment to re-measure the proton charge radius (PRad-II) experiment at Jefferson Lab. The result from the PI’s first experiment (PRad) agreed with the small radius from muonic hydrogen spectrometry measurements and played a critical role in the recent revision of the CODATA recommendation for the proton radius. During the grant period the PI and his group will develop, construct, test and install new detection systems to improve the results of the first experiment by a factor of four. This will be the most accurate measurement of the proton radius performed with the electron-proton scattering experiments. With this accuracy the PRad-II experiment will address the current difference between the PRad and other electron-proton scattering results.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.