[en] The HAPPEx-II experiment at Thomas Jefferson National Accelerator Facility measures the parity-violating helicity-correlated scattering asymmetry APV in elastic electron scattering from 1H and 4He. These measurements explore the strange quark contributions to the electric and magnetic vector form factors View the MathML source and View the MathML source of the nucleon. An introduction to the experimental technique and preliminary results from an initial run of these experiments in summer 2004 are presented.

[en] The PS185 experiment at LEAR has produced a wealth of high precision measurements of cross-sections and final state polarization observables in near-threshold antihyperon-hyperon production from antiproton-proton annihilation. In its most recent run, PS185/3 extended its capabilities by utilizing a transversely polarized frozen spin target to measure exclusive Λ-barΛ production. This allows access to a broad set of spin observables involving initial state spin. Competing theoretical models for this reaction have differing predictions for some of these newly-accessible spin observables, most notably the depolarization D_nn. This data is expected to provide a rigorous test of these models. Current results from the analysis of this data are presented

[en] The simplest models might describe the nucleon as 3 light quarks, but this description would be incomplete without inclusion of the sea of glue and q q-bar pairs which binds it. Early indications of a particularly large contribution from strange quarks in this sea to the spin and mass of the nucleon motivated an experimental program examining the role of these strange quarks in the nucleon vector form factors. The strangeness form factors can be extracted from the well-studied electromagnetic structure of the nucleon using parity-violation in electron-nuclear scattering to isolate the effect of the weak interaction. With high luminosity and polarization, and a very stable beam due to its superconducting RF cavities, CEBAF at Jefferson Lab is a precision instrument uniquely well suited to the challenge of measurements of the small parity-violating asymmetries. The techniques and results of the two major Jefferson Lab experimental efforts in parity-violation studies, HAPPEX and G0, as well as efforts to describe the strange form factors in QCD, will be reviewed.

[en] Polarized electron beams have played an important role in scattering experiments at moderate to high beam energies. Historically, these experiments have been primarily targeted at studying hadronic structure - from the quark contribution to the spin structure of protons and neutrons, to nucleon elastic form factors, as well as contributions to these elastic form factors from (strange) sea quarks. Other experiments have aimed to place constraints on new physics beyond the Standard Model. For most experiments, knowledge of the magnitude of the electron beam polarization has not been a limiting systematic uncertainty, with only moderately precise beam polarimetry requirements. However, a new generation of experiments will require extremely precise measurements of the beam polarization, significantly better than 1%. This article will review standard electron beam polarimetry techniques and possible future technologies, with an emphasis on the ever-improving precision that is being driven by the requirements of electron scattering experiments.

[en] An experimental study of the 16O(e, e'K+)16N_#Lambda# reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e, e'K+)Λ,Σ₀ exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76 ± 0.16 MeV was obtained for 16N_#Lambda# with better precision than previous measurements on the mirror hypernucleus 16O_#Lambda#. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p1/2 and p3/2 hole states of the 15N core nucleus.

[en] We describe the research and development work for the P2 experiment which aims for a high precision determination of the weak mixing angle sin² θ_W to a precision of 0.15% at a four-momentum transfer of 4.5 x 10^-3 GeV². This accuracy, comparable to existing measurements at the Z pole, allows for a sensitive test of the Standard Model up to a mass scale of 50 TeV, extendable to 60 TeV. The weak mixing angle is connected to the weak charge of the proton which will be extracted from a measurement of the parity violating cross section asymmetry -39.94 x 10^-9 in elastic electron-proton scattering. A total accuracy of 0.57 x 10^-9 is achievable in a measurement time of 11000 h using a 150 μA polarized electron beam impinging on a 60 cm liquid hydrogen target. The P2 asymmetry is smaller than any asymmetry measured so far in electron scattering with an unprecedented goal for the accuracy. The use of a solenoid spectrometer with 100% φ-acceptance as well as an atomic hydrogen trap polarimeter are new features, which have never before been used in parity-violation experiments. In order to collect the enormous statistics required for this measurement, the new Mainz Energy-Recovering Superconducting Accelerator (MESA) is under construction. Plans for the associated beam control system and the polarimetry are described in this article as well. A liquid hydrogen high-power target with an extremely low noise level of 10 ppm needs to be designed and constructed. We report in addition on the conceptual design of the P2 spectrometer, its Cherenkov detectors, the integrating read-out electronics as well as the ultra-thin, fast tracking detectors. The physics program of the MESA facility comprises indirect, high precision search for physics beyond the Standard Model, measurement of the neutron distribution in nuclear physics, single-spin asymmetries, and a possible future extension to the measurement of hadronic parity violation. (orig.)