[en] Precision electroweak experiments with polarized electrons

[en] HAPPEX is a new experiment to probe the strange structure of the nucleon with parity violating electron scattering. We describe the physics motivation, provide an experimental overview and report on the results from the first data run. The asymmetry for the elastic scattering of 3.3 GeV electrons off target protons at a scattering angle of 12.5 degrees was measured to a precision of 15% of itself. The contribution from strange quark form factors was found to be zero within the experimental and theoretical uncertainties

[en] We discuss the current status and prospects of an experimental program of parity-violating asymmetry measurements in the scattering of longitudinally polarized electrons off unpolarized fixed targets. In particular, we focus on those measurements where judicious choices of target species and kinematics allows the theoretical predictions to be made purely in terms of fundamental electroweak couplings with little theoretical uncertainty. If such asymmetries are measured with sufficient precision, they are sensitive to new physics at the TeV scale. After reviewing recent results, two new experimental initiatives called MOLLER and SoLID being designed for the Jefferson Laboratory 12 GeV upgrade are discussed.

[en] Parity-violating electron scattering has developed into a precise and sensitive tool to probe the structure of weak neutral current interactions at Q²<< M_Z². Steady improvements in experimental techniques have made feasible asymmetry measurements with precision approaching 10 parts per billion and fractional accuracy of a few percent. In the future, upgrades of new facilities, new laboratories and further refinements of experimental techniques should allow us to explore new aspects of the strong and electroweak interactions. We describe some of these ideas in this article. (orig.)

[en] We have carried out a precision of the parity-violating asymmetry APV in the scattering of longitudinally polarized electrons off electrons in a liquid hydrogen target. The measurement was performed with the 50 GeV beam line at SLAC. The final result with the full data set collected in three production runs is APV = - 131 ± 14 (stat) ± 10 (syst) parts per billion. The result leads to new limits on possible contact interactions at the TeV scale

[en] We discuss the status and prospects of an experimental program of parity-violating asymmetry measurements in the scattering of longitudinally polarized electrons off unpolarized fixed targets. In particular, we focus on those measurements where judicious choices of target and kinematics allows the theoretical predictions to be made purely in terms of fundamental electroweak couplings. If such asymmetries are measured with sufficient precision, they are sensitive to new physics at the TeV scale. The physics implications of recent results, experiments under construction and plans for the future are discussed.

[en] We discuss the status and prospects of an experimental program of parity-violating asymmetry measurements in the scattering of longitudinally polarized electrons off unpolarized fixed targets. One thrust is the measurements of nucleon neutral weak form factors at intermediate four-momentum transfer (0.1 < Q2 < 1) (GeV/c)2 which provide information about the role of virtual strange quarks on the charge and current distributions inside nucleons. A new topic is the elastic neutral weak amplitude from scattering off a heavy spinless nucleus, which is sensitive to the presence of a neutron skin. Finally, we discuss the neutral current elastic amplitude at very low Q2, which allows precision measurements of the weak mixing angle at low energy and is thus sensitive to new physics at the TeV scale. The physics implications of recent results, potential measurements from experiments under construction as well as new ideas at future facilities are discussed

[en] We report on a mature experimental program to measure the parity violating asymmetry in the elastic scattering of longitudinally polarized electrons from unpolarized 1H, 2H, 4He and 208Pb targets. One focus is the measurement of the nucleon neutral weak form factors at intermediate four-momentum transfer (0.1 < Q2 < 1) (GeV/c)2 which provide information about the impact of virtual strange quarks on the charge and current distributions inside nucleons. Another focus is the neutral current elastic amplitude at very low Q2, which can provide stringent tests of the standard model and possess unique sensitivity to new physics at the TeV scale. Finally, the elastic neutral weak amplitude from scattering off a heavy spinless nucleus is very sensitive to the presence of a neutron skin. We report on recent technical progress in the design and scope of the experimental techniques. The physics implications of the published measurements are discussed and the current status and anticipated results experiments under construction are summarized

[en] Precision measurements of electroweak observables at Q²<< M_Z² complement high energy collider experiments in order to comprehensively search for new dynamics at the TeV scale. Parity-violating electron scattering is one promising technique that has demonstrated the potential to achieve sufficient precision, and which has unique sensitivity to TeV scale dynamics. In particular, we discuss parity-violating electron-electron (Moeller scattering). After reviewing the completed SLAC E158 experiment, we discuss a new project to improve on the SLAC measurement by a factor of 5 using the upgraded 12 GeV beam at Jefferson Laboratory, allowing a measurement of the weak mixing angle sin ²θ_W with comparable precision to the single best measurement at e⁺e^- colliders, and thus accessing the contact interaction scale Λ_ee∼25 TeV.

[en] Measurements of electroweak observables at Q² << M_Z², if carried out with sufficient accuracy, complement potential discoveries at the Large Hadron Collider. Such measurements will be necessary in order to comprehensively search for new dynamics at the TeV scale. We discuss the new MOLLER project to make a precision measurement of parity-violation in Møller scattering using the upgraded 11 GeV beam at Jefferson Laboratory. This would allow a measurement of the weak mixing angle sin²θ_W with comparable precision to the single best measurement at e⁺e− colliders, and accesses the contact interaction scale Λ_ee∼25 TeV.