A Program of Medium Energy Nuclear Physics

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UIUC PROJECT ABSTRACTThe NSF-supported Program of Medium Energy Nuclear Physics will allow the nuclear physics group at the University of Illinois at Urbana-Champaign to continue to lead and contribute to high-impact experiments in international nuclear physics research. The research program fea-tures two central themes, namely 1) The structure and interactions of nucleons and nuclei; and 2) Tests of fundamental symmetries and the standard model. Specific activities include the estab-lished international experiments: G0, HERMES, PHENIX, RCS, Muon g-2, Lan, and Cap. Additionally, the group has a local feasibility effort in hydrogen atomic parity violation (H-APV) and is helping to develop a new neutron electric dipole moment (n-EDM) experiment. The goal of all of these experiments is to help answer important questions in subatomic physics. For ex-ample, in G0, HERMES, RCS and the PHENIX spin program, a common query is "How is the proton built?" The experiments use different tools such as parity-violating electron scattering, polarized electron-nucleon scattering, real Compton scattering, and polarized proton-proton col-lisions to discover the roles that constituent quarks, sea quarks and gluons (the partons) play to result in the well-known properties of the proton. The experiments should help settle the debate about how the proton obtains its half-integer spin. They will also shed light on the relative im-portance of different types of quarks inside the proton revealing, for example, how strange quarks contribute to the proton's charge and magnetic structure. In the PHENIX program at RHIC, deuteron-nuclei collisions will also be studied to investigate the role that partons play in nuclei. The Muon g-2, H-APV, and n-EDM activities are all aimed at the second theme, asking the question "Is the current standard model correct?" The most mature of these efforts, g-2, has already provided exciting and suggestive evidence that some type of standard model extension might be required. Completion of this effort and possible extensions will provide either a very stringent limit on new physics or, alternatively, a strong indication that it must be present. Other precision measurements of fundamental parameters are featured in the ULan and UCap experi-ments. The first of these will determine the muon lifetime to a precision of one part per million, which can then be interpreted as a 20-fold improvement in the determination of the weak interac-tion strength. The second experiment will accurately measure the least-well-known weak form factor (gP) of the proton. This will provide a stringent test of precise theoretical predictions founded on basic symmetries of strong interactions at low energies. In addition to direct physics research out-comes, the group has reached beyond the laboratory to make significant contributions to educa-tion and outreach and will continue to do so. Research projects contribute substantially to the education of a large number of postdocs, graduate, and undergraduate students.