[en] Precision electron beam polarimetry is becoming increasingly important as parity violation experiments attempt to probe the frontiers of the standard model. In the few GeV regime, Moeller polarimetry is well suited to high-precision measurements, however is generally limited to use at relatively low beam currents (< 10 (micro)A). We present a novel technique that will enable precision Moeller polarimetry at very large currents, up to 100 (micro)A

[en] We propose to measure pion electroproduction off ¹H, ², ¹²C, ⁶⁴Cu, and ¹⁹⁷Au, and extract the pion transparency through the nuclear medium between Q² = 1 and 5 (GeV/c)². The pion transparency is predicted to be a signature of the onset of nuclear filtering and/or Color Transparency. Recent experiments have reported evidence for Color Transparency effects at Q² approx 10 (GeV/c)². The occurrence of nuclear filtering could potentially explain the apparent discrepancy between (proton) nuclear transparencies found in quasielastic A(e,e'p) and A(p,2p) experiments. The occurrence of these effects is an effective signature of the approach to the factorization regime in meson electroproduction experiments, necessary for the access to Generalized Parton Distributions. Measurable effects of approx. 40% are predicted for this region of Q². The proposed experiment seeks to measure the pion transparency with 5-10% uncertainties, dominated by systematics, up to Q² = 5 (GeV/c)²

[en] We measured the angular dependence of the three recoil proton polarization components in two-body photodisintegration of the deuteron at a photon energy of 2 GeV. These new data provide a benchmark for calculations based on quantum chromodynamics. Two of the five existing models have made predictions of polarization observables. Both explain the longitudinal polarization transfer satisfactorily.. Transverse polarizations are not well described, but suggest isovector dominance

[en] We report the results of a new Rosenbluth measurement of the proton form factors at Q² values of 2.64, 3.20 and 4.10 GeV². Cross sections were determined by detecting the recoiling proton in contrast to previous measurements in which the scattered electron was detected. At each Q², relative cross sections were determined to better than 1%. The measurement focused on the extraction of G_E/G_M which was determined to 4-8% and found to approximate form factor scaling, i.e. μ_pG_E ∼ G_M. These results are consistent with and much more precise than previous Rosenbluth extractions. However, they are inconsistent with recent polarization transfer measurements of comparable precision, implying a systematic difference between the two techniques

[en] The coherent 3He(e,eπ+)3H reaction was measured at Q2 = 0.4 (GeV/c)2 and W = 1.6 GeV for two values of the virtual photon polarization, ε, allowing the separation of longitudinal and transverse cross sections. The results from the coherent process on 3He were compared to H(e,eπ+)n data taken at the same kinematics. This marks the first direct comparison of these processes. At these kinematics (pπ = 1.1 GeV/c), pion rescattering from the spectator nucleons in the 3He(e,eπ+)3H process is expected to be small, simplifying the comparison to π+ production from the free proton

[en] The RSS collaboration has measured the spin structure functions g₁ and g₂ of the proton at Jefferson Lab using the lab's polarized electron beam, the Hall C HMS spectrometer and the UVa polarized solid target. The asymmetries A_parallel and A_perp were measured at the elastic peak and in the region of the nucleon resonances (1.085 GeV < W < 1.910 GeV) at an average four momentum transfer of Q² = 1.3 GeV². The extracted spin structure functions and their kinematic dependence make a significant contribution in the study of higher-twist effects and polarized duality tests

[en] We have measured the nuclear transparency of the A(e,e' pi⁺) process in ²H,¹²C, ²⁷Al, ⁶³Cu and ¹⁹⁷Au targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range Q² = 1.1 - 4.7 (GeV/c)². The nuclear transparency was extracted as the super-ratio of σ_Aσ_H from data to a model of pion-electroproduction from nuclei without pi-N final state interactions. The Q² and atomic number dependence of the nuclear transparency both show deviations from traditional nuclear physics expectations, and are consistent with calculations that include the quantum chromodynamical phenomenon of color transparency

[en] The quasielastic (e,e[prime]p) reaction was studied on targets of deuterium, carbon, and iron up to a value of momentum transfer Q2 of 8.1 (GeV/c)2. A nuclear transparency was determined by comparing the data to calculations in the plane-wave impulse approximation. The dependence of the nuclear transparency on Q2 and the mass number A was investigated in a search for the onset of the color transparency phenomenon. We find no evidence for the onset of color transparency within our range of Q2. A fit to the world's nuclear transparency data reflects the energy dependence of the free-proton-nucleon cross section

[en] The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at theta_cm = 37^o are consistent with the constituent counting rules for E_gamma∼> 4 GeV, while those at 70^o are consistent with the constituent counting rules for E_gamma ∼> 1.5 GeV