The interpretation of parity-violating electron-scattering experiments

Abstract

The theoretical interpretation of several prospective intermediate-energy parity-violating (p.v.) electron-scattering experiments is discussed. Particular attention is paid to the interplay of various sources of theoretical hadronic-physics uncertainties. It is argued that these uncertainties may render high-precision, p.v. electron scattering less suitable for standard-model tests than atomic parity-violation experiments. However, p.v. electron scattering offers a unique window on various aspects of nucleon and nullear structure, such as the presense of strange quarks in the nucleon. In particular, it is found that a series of measurements on the protoon could provide interesting constraints on the two strangeness vector-current form factors, although not to the degree needed to permit a 1% extraction of the weak mixing angle. The prospects for further tightening these constraints with elastic scattering from the ( J π , T) = ( o +, 0) targets and from the deuteron are evaluated in detail. Associated, unresolved theoretical issues are highlighted, and the relationship between theoretical interpretability and experimental doability is analyzed. These considerations are applied to three recent proposals for experiments at CEBAF. A treatment of quasielastic p.v. electron scattering is also given, including a reanalysis of the recent Mainz 9Be( e , e′) measurement to account for radiative-correction uncertainties in the quoted value of the weak mixing angle. For each case considered, the kinematic conditions are identified for which interpretability of a prospective experiment might be optimized.