Precision Study of the Radiative Decay Widths of Light Pseudoscalar Mesons via the Primakoff Effect

北卡罗来纳a&t州立大学（NCAT）的核物理小组在托马斯·杰斐逊国家加速器设施（JLab）的PrimEx实验项目中发挥了主导作用。该项目的目的是测试当代物理学中物质核相互作用理论中对称破缺现象的基本影响。这将通过以前所未有的精度测量两种最轻的基本粒子——中性介子和介子的衰变概率来实现。这些亚原子粒子是自然界中已知的最轻的粒子，由物质的更基本成分——夸克组成。因此，该理论的预测更加准确，并且对这些粒子的衰变过程的模型依赖性更小。这个项目的第一个实验，中性介子的衰变概率，是在过去几年里发展起来的，并在2004年秋天成功地执行了。收集了丰富、高统计量的实验数据集。PrimEx合作项目目前正在分析数据，以高精度提取中性介子寿命。我们期望这些结果，预期准确度为1.5%，将作为我们对物质与辐射相互作用的理解中左右对称破缺现象水平的最终测试。该项目的第二阶段包括对两个辐射粒子（光子）的介子衰变过程进行高精度测量。我们期望，随着JLab能量的加倍（12 gev升级项目），我们将能够进行一个比以前的实验有显著改善的不确定性的实验。本实验的结果可能会消除目前两类不同实验数据集之间的差异。由此，它将对确定当前粒子数据手册中介子部分更精确的衰变概率产生重大影响。这将导致以一种直接和独立于模型的方式提取轻夸克的相对质量。北卡罗来纳农工州立大学是一所历史悠久且以非裔美国人为主的大学。核物理小组的研究活动对NCAT社区产生了重大影响。这个项目让我们的研究生和本科生都有机会从事世界一流的实验研究。我们有5名研究生和8名本科生参与了这项研究。在研究生中，有4人（包括两名非裔美国男性和一名女性）已经成功地为他们的硕士学位论文辩护。我们希望研究生和本科生都能继续参与PrimEx项目。在不久的将来，这种参与将在数据分析领域，以帮助实现实验的最终目标。他们所从事的研究大大提高了本科生和研究生进入竞争激烈的研究生项目的能力。这一点尤其重要，因为来自传统上代表性不足的群体的美国人获得物理学硕士和博士学位的人数极低。

The nuclear physics group at North Carolina A&T State University (NCAT) has the lead role in the PrimEx experimental project at the Thomas Jefferson National Accelerator Facility (JLab). The aim of this project is to test the fundamental effects of symmetry breaking phenomena in the theory of the nuclear interaction of matter in contemporary physics. This will be achieved through measuring with unprecedented precisions the decay probabilities of two of the lightest elementary particles the neutral pion and the eta-meson. These subatomic particles are the lightest particles known in nature that consist of the more fundamental constituents of matter, the quarks. Therefore, the predictions of the theory are more accurate and much less model dependent for the decay processes of these particles. The first experiment in this project, the decay probability of the neutral pions, was developed in the past several years and successfully executed in the fall of 2004. A rich and high statistics experimental data set has been collected. The PrimEx collaboration is currently analyzing the data to extract the neutral pion lifetime with a high precision. We expect that these results, with an anticipated 1.5% accuracy, will serve as an ultimate test of the level of the left-right symmetry breaking phenomena in our understanding of the interaction of matter with the radiation. The second stage of this project includes the high precision measurement of the eta-meson decay process in to two particles of radiation (the photons). We expect that, with the doubling of the JLab energies (the 12-GeV upgrade project), we will be able to perform an experiment with significantly improved uncertainties over previous experiments. The results of this experiment will possibly remove the current discrepancy between two types of different experimental data sets. With that, it will make a significant impact in the determination of more precise decay probabilities in the eta-meson sector of the current Particle Data Book. This will lead to the extraction of the relative masses of the light quarks in a direct and model independent way. North Carolina A&T State University is a historically and predominately African-American institution. The research activities of the nuclear physics group have had a significant impact on the NCAT community. This project has given both our graduate and undergraduate students the opportunity to engage in world class experimental research. We have had 5 graduate and 8 undergraduate students engaged in this research. Of the graduate students, 4 (including two African American males and one female) have now successfully defended their Masters Degree theses. We expect to continue to have both graduate and undergraduate students participate in the PrimEx project. In the near future, this participation will be in the realm of data analysis to help achieve the ultimate goal of the experiment. The research they engage in greatly enhances the ability of both the undergraduate and graduate students to be accepted into competitive graduate programs. This is especially important in light of the extremely low number of M.S. and Ph.D. degrees in physics held by Americans from traditionally underrepresented groups.