Studies of the Structure of Light Mesons and Nucleons through Exclusive Reactions

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Pions and kaons are the lightest subatomic particles and play a unique role in nature; our understanding of them is essential for explaining the fundamental structure of matter. This research is centered on precision measurements of pion and kaon properties that have the potential to reveal the three-dimensional structure of the nucleons, the protons and neutrons that, together with their interactions, generate nearly of the mass of the visible universe. As such, this work probes the fundamental structure of that part of the universe that we can see. This project is part of a series of experiments taking place at the Thomas Jefferson National Accelerator Laboratory. Early career scientists, graduate students, and undergraduate students play an integral part in this project, which provides them with opportunities to further develop their training and education. These include gaining experience in the design, assembly, and testing of modern instrumentation for the detection of radiation and subatomic particles and fast signal processing electronics, and in analyzing scientific data. Furthermore, learning to work in a large international scientific community will prepare early career scientists and students for the modern work environment at academic institutions, national laboratories, and industry. This program is focused on precision measurements of pion and kaon form factors and structure functions, and validation of our understanding of hard exclusive and semi-inclusive reactions towards 3D hadron imaging and potential future flavor decomposition. Form factors are the most basic quantity towards understanding transverse spatial structure. The structure functions are expected to be different for pions, kaons, and nucleons regarding sea quarks and gluons and provide basic information about the origin of mass. 3D hadron imaging allows for the extraction of correlations between quark longitudinal momentum and transverse position from the experiment using factorization theorems. To validate the meson factorization theorems and potential future flavor decomposition, one has to measure the longitudinal and transverse (L/T) separated cross sections. This project plays a central role in this effort through precision pion, and kaon L/T separated cross section measurements at the 12 GeV Jefferson Lab and development of measurements of the, to date, mostly unknown pion and kaon structure functions at a potential future Electron-Ion Collider.