[en] The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the parity-violating asymmetry in elastic scattering at very low Q² of a longitudinally polarized electron beam on a proton target. The experiment will measure the weak charge of the proton, and thus the weak mixing angle at low energy scale, providing a precision test of the Standard Model. Since the value of the weak mixing angle is approximately 1/4, the weak charge of the proton Q_w^p = 1-4 sin² θ_w is suppressed in the Standard Model, making it especially sensitive to the value of the mixing angle and also to possible new physics. The experiment is approved to run at JLab, and the construction plan calls for the hardware to be ready to install in Hall C in 2007. The theoretical context of the experiment and the status of its design are discussed

[en] Separated longitudinal and transverse structure functions for the reaction 1H(e,eprime pi+)n were measured in the momentum transfer region Q2=0.6-1.6 (GeV/c)**2 at a value of the invariant mass W=1.95 GeV. New values for the pion charge form factor were extracted from the longitudinal cross section by using a recently developed Regge model. The results indicate that the pion form factor in this region is larger than previously assumed and is consistent with a monopole parameterization fitted to very low Q2 elastic data

[en] The data analysis for the reaction H(e,e(prime) pi⁺)n, which was used to determine values for the charged pion form factor Fpi for values of Q2 = 0.6-1.6 (gEv/C)², has been repeated with careful inspection of all steps and special attention to systematic uncertainties. Also the method used to extract Fpi from the measured longitudinal cross section was critically reconsidered. Final values for the separated longitudinal and transverse cross sections and the extracted values of Fpi are presented

[en] A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data

[en] Tensor polarization observables (t20, t21 and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)². The experiment was performed at the Jefferson Laboratory in Hall C using the electron HMS Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q² the deuteron charge form factors G_C and G_Q. They are in good agreement with relativistic calculations and disagree with pQCD predictions

[en] Separated longitudinal and transverse cross sections for charged pion electroproduction from ¹H, ²H, and ³He were measured at Q² = 0.4 (GeV/c)² for two values of the invariant mass, (bar W) = 1.15 GeV and (bar W) = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in ^3>He at (bar W) = 1.60 GeV. The (bar W) = 1.15 GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production

[en] We report the first measurement using a solid polarized target of the neutron electric form factor Gⁿ_E via d-vector(e-vector, e'n)p. Gⁿ_E was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia (¹⁵ND₃). The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility in quasifree kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find Gⁿ_E = 0.04632±0.00616(stat)±0.00341(syst) at Q² = 0.495 (GeV/c)²

[en] The Jefferson Laboratory E93-038 collaboration conducted measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, GⁿE/GⁿM, via recoil polarimetry from the quasielastic ²H((rvec e),e/(rvec n))¹H reaction at three values of Q² [viz., 0.45, 1.15, and 1.47 (GeV/c)²] in Hall C of the Thomas Jefferson National Accelerator Facility. The preliminary results for GⁿE at Q² = 0.45 and 1.15 (GeV/c)² are consistent with the Galster parameterization; however, the preliminary result for GⁿE at Q² = 1.47 (GeV/c)² lies slightly above the Galster parameterization

[en] The ratio of the electric to the magnetic form factor of the neutron, G_En/G_Mn, was measured via recoil polarimetry from the quasielastic d((pol-e),e(prime)(pol-n)p) reaction at three values of Q² [viz., 0.45, 1.15 and 1.47 (GeV/c)²] in Hall C of the Thomas Jefferson National Accelerator Facility. Preliminary data indicate that G_En follows the Galster parameterization up to Q² = 1.15 (GeV/c)² and appears to rise above the Galster parameterization at Q² = 1.47 (GeV/c)²

[en] We report values for the neutron electric to magnetic form factor ratio, G_En/G_Mn, deduced from measurements of the neutron's recoil polarization in the quasielastic ²H((rvec e), e(prime)(rvec n)) ¹H reaction, at three Q² values of 0.45, 1.13, and 1.45 (GeV/c)². The data at Q² = 1.13 and 1.45 (GeV/c)² are the first direct experimental measurements of GEn employing polarization degrees of freedom in the Q² > 1 (GeV/c)² region and stand as the most precise determinations of GEn for all values of Q²