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

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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.