The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved

High-precision 1H(e,e'p)pi(0) measurements at Q2 = 0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma*N-->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole ( I = 3/2) amplitude ratios, R(SM) = (-6.5+/-0.2(stat+sys)+/-2.5(mod))% and R(EM) = (-2.1+/-0.2(stat+sys)+/-2.0(mod))%, are dominated by model error. Previous R(SM) and R(EM) results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.

We have measured the cross section for quasielastic 1p-shell proton knockout in the 16O(e,e(')p) reaction at omega = 0.439 GeV and Q2 = 0.8 (GeV/c)(2) for missing momentum P(miss)

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We present a measurement of the induced proton polarization P n in 0 electroproduction on the proton around the ⌬ resonance. The measurement was made at a central invariant mass and a squared four-momentum transfer of Wϭ1231 MeV and Q 2 ϭ0.126 GeV 2 /c 2 , respectively. We measured a large induced polarization, P n ϭϪ0.397Ϯ0.055Ϯ0.009. The data suggest that the scalar background is larger than expected from a recent effective Hamiltonian model. ͓S0556-2813͑98͒02012-3͔ PACS number͑s͒: 13.88.ϩe, 13.60.Le, 13.60.Rj, 14.20.Gk At low Q 2 , the N→⌬ transition is dominated by the magnetic dipole amplitude. In a simple SU͑6͒ model in which all the quarks occupy S states in the N and ⌬ wave functions, the N→⌬ transition is a spin flip of a single quark. If the quarks are allowed to occupy D states as well as S states in the N or ⌬ wavefunctions, then electric and Coulomb quadrupole transitions are allowed ͓1,2͔. The ratios of these quad-*Present address: