Parity Violating Electron Scattering at Jefferson Lab

0072283 Johnston Understanding the structure of the nucleon at the quark level is of fundamental importance in particle and nuclear physics. An observable identified as being directly sensitive to quark degrees of freedom is the cross section difference between the elastic scattering of electrons with polarizations parallel and antiparallel to the incident electron momentum from unpolarized protons. This parity violating asymmetry results from the interference between the process in which an incident electron exchanges a photon and the one in which it exchanges a neutral weak boson. Specifically, parity violating elastic electron proton scattering allows determination of the nucleon strange charge and magnetic form factors, which describe the contributions from strange quarks to the nucleon, along with their momentum transfer dependence. If parity violating electron nucleon scattering experiments are extended beyond the elastic channel into particular inelastic channels, additional information about the quark currents inside the nucleon can clearly be obtained. Understanding the Delta resonance, the first excited nucleon state, has always been considered an important test of nucleon structure models. The parity violating asymmetry in electroproduction of this resonance can isolate the isovector contributions to the quark currents. The Delta resonance can also be produced in electron scattering via the exchange of the neutral weak boson. Thus, weak transition form factors also contribute to the N-to-Delta transition. Included in the research efforts of the Louisiana Tech Center for Applied Physics Studies (CAPS) is the study of parity violating electron scattering in both elastic and inelastic reactions. CAPS has significant involvement in the G0 experiment at Jefferson Lab (E00-006), which will investigate the elastic channel, and are spokespersons for experiment E97-104, ``Measurement of the Parity Violating Asymmetry in the N-to-Delta transition.''