Parity Violating Electron Scattering at Jefferson Lab

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0072283Johnston Understanding the structure of the nucleon at the quark level is offundamental importance in particle and nuclear physics. An observableidentified as being directly sensitive to quark degrees of freedom isthe cross section difference between the elastic scattering of electronswith polarizations parallel and antiparallel to the incident electronmomentum from unpolarized protons. This parity violating asymmetryresults from the interference between the process in which an incidentelectron exchanges a photon and the one in which it exchanges a neutralweak boson. Specifically, parity violating elastic electron protonscattering allows determination of the nucleon strange charge andmagnetic form factors, which describe the contributions from strangequarks to the nucleon, along with their momentum transfer dependence.If parity violating electron nucleon scattering experiments are extendedbeyond the elastic channel into particular inelastic channels,additional information about the quark currents inside the nucleon canclearly be obtained. Understanding the Delta resonance, the firstexcited nucleon state, has always been considered an important test ofnucleon structure models. The parity violating asymmetry inelectroproduction of this resonance can isolate the isovectorcontributions to the quark currents. The Delta resonance can also beproduced in electron scattering via the exchange of the neutral weakboson. Thus, weak transition form factors also contribute to theN-to-Delta transition. Included in the research efforts of the Louisiana Tech Center forApplied Physics Studies (CAPS) is the study of parity violating electronscattering in both elastic and inelastic reactions. CAPS hassignificant involvement in the G0 experiment at Jefferson Lab (E00-006),which will investigate the elastic channel, and are spokespersons forexperiment E97-104, ``Measurement of the Parity Violating Asymmetry inthe N-to-Delta transition.''