Study of the Electroweak Structure of the Nucleon

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This project seeks answers to two of the overarching questions central to nuclear physics: "How does subatomic matter organize itself and what phenomena emerge?", and "Are the fundamental interactions that are basic to the structure of matter fully understood?". The Standard Model (SM) of particle physics is successful at describing interactions of elementary particles, but it is known to be incomplete, because the SM fails to describe phenomena that shape our universe, like the difference between matter and anti-matter or the nature of dark matter. Furthermore, the mechanisms by which the strong force binds three light elementary particles, quarks, to make massive composite particles, proton and neutrons, are not well understood quantitatively. Over ninety nine percent of the mass of the visible matter in the universe is generated by the strong force in this way. In this context, the PIs are involved in two experimental programs using the electron beam at the Thomas Jefferson National Accelerator Facility, first to investigate the internal structure of the proton as a means of investigating the nature of the strong force, and second to search for physics beyond the Standard Model by performing precision measurements of interactions with precise Standard Model predictions. The PIs will train two graduate students and undergraduate students in carrying out the research program, and will engage in STEM outreach activities through the "Adopt a physicist" program. This project will support in part the use of Deeply Virtual Compton Scattering of electrons from the proton to produce a 3-D tomographic picture of the internal structure of the proton against which models of the strong force can be tested. Roche is one of the spoke persons for experiment E12-06-114 at JLab, and this project will support the data taking and data analysis for this experiment. The immediate goal of this experiment is to test the hypothesis of scaling on which the Generalized Parton Distribution formalism used to interpret this kind of experiments is based. The second project supported by this award will further the involvement of the PIs and their students in the JLab parity violating electron scattering experiments, QWEAK and MOLLER. These experiments test the Standard Model by studying the electromagnetic and weak forces in electron-proton and electron-electron scattering. The PIs will continue their work with QWEAK up to publication of the final results, and will use their expertise in data acquisition and software development for the preparation of the MOLLER experiment.