[en] The physic program at CEBAF Hall A includes several experiments using 4 GeV polarized electron beam: parity violation in electron elastic scattering from proton and ⁴He, electric form factor of the proton by recoil polarization, neutron spin structure function at low Q². Some of these experiments will need beam polarization measurement and monitoring with an accuracy close to 4%, for beam currents ranging from 100 nA to 100 microA. A project of a Compton Polarimeter that will meet these requirements is presented. It will comprise four dipoles and a symmetric cavity consisting of two identical mirrors. 1 fig., 10 refs

[en] Light-weight spherical mirrors have been appositely designed and built for the gas threshold Cherenkov detectors of the two Hall A spectrometers. The mirrors are made of a 1mm thick aluminized plexiglass sheet, reinforced by a rigid backing consisting of a phenolic honeycomb sandwiched between two carbon fiber mats epoxy glued. The produced mirrors have a thickness equivalent to 0.55% of radiation length, and an optical slope error of about 5.5mrad. These characteristics make these mirrors suitable for the implementation in Cherenkov threshold detectors. Ways to improve the mirror features are also discussed in view of their possible employment in RICH detectors

[en] In one of the first measurements of its type, the nuclear response function R_LT has been determined in the ¹⁶O(e,e'p)¹⁵N reaction in quasielastic kinematics for the ground state (1/2^-) and the first excited state (6.32 MeV, 3/2^-). Extracted momentum distributions for these two states exhibit asymmetric behavior. Spectroscopic factors show significant depletion of strength, consistent with previous results. R_LT agrees better with relativistic distorted-wave impulse-approximation calculations in magnitude than does the total cross section

[en] We have measured the spin structure functions g₁ and g₂ of ³He in a double-spin experiment by inclusively scattering polarized electrons at energies ranging from 0.862 to 5.07 GeV off a polarized ³He target at a 15.5^o scattering angle. Excitation energies covered the resonance and the onset of the deep inelastic regions. We have determined for the first time the Q² evolution of Γ₁(Q²)=/int₀¹ g₁(x,Q²) dx, Γ₂(Q²)=/int₀¹ g₂(x,Q²) dx and d₂ (Q²) = /int₀¹ x ²[2g₁(x,Q²) + 3g₂(x,Q²)] dx for the neutron in the range 0.1 GeV² /leq Q² /leq 0.9 GeV² with good precision. Γ₁(Q²) displays a smooth variation from high to low Q². The Burkhardt-Cottingham sum rule holds within uncertainties and d₂ is non-zero over the measured range

[en] The ratio of the proton's elastic electromagnetic form factors, G_Ep/G_Mp, was obtained by measuring P_t and P_ell, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic (rvec e)p → e(rvec p) reaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV². In the single photon exchange approximation, the ratio G_Ep/G_Mp is directly proportional to the ratio P_t/P_ell. The simultaneous measurement of P_t and P_#ell# in a polarimeter reduces systematic uncertainties. The results for the ratio G_Ep/G_Mp show a systematic decrease with increasing Q², indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been reanalyzed and systematic uncertainties have become significantly smaller than previously published results

[en] The deuteron elastic structure function A(Q²) has been extracted in the range 0.7 < or = Q² < or = 6.0 (GeV/c)² from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models, based on the impulse approximation with the inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamics