[en] We describe a new aerogel threshold Cherenkov detector installed in the HMS spectrometer in Hall C at Jefferson Lab. The Hall C experimental program in 2003 required an improved particle identification system for better identification of π/K/p, which was achieved by installing an additional threshold Cherenkov counter. Two types of aerogel with n = 1.03 and n = 1.015 allow one to reach ∼10^-3 proton and 10^-2 kaon rejection in the 1-5 GeV/c momentum range with pion detection efficiency better than 99% (97%). The detector response shows no significant position dependence due to a diffuse light collection technique. The diffusion box was equipped with 16 Photonis XP4572 PMT's. The mean number of photoelectrons in saturation was ∼16 and ∼8, respectively. Moderate particle identification is feasible near threshold

[en] The ¹H(e,e(prime)π⁺)n cross section was measured for a range of four-momentum transfer up to Q²=3.91 GeV² at values of the invariant mass, W, above the resonance region. The Q²-dependence of the longitudinal component is consistent with the Q²-scaling prediction for hard exclusive processes. This suggests that perturbative QCD concepts are applicable at rather low values of Q². Pion form factor results, while consistent with the Q²-scaling prediction, are inconsistent in magnitude with perturbative QCD calculations. The extraction of Generalized Parton Distributions from hard exclusive processes assumes the dominance of the longitudinal term. However, transverse contributions to the cross section are still significant at Q²=3.91 GeV²

[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] The ratio of the electric to the magnetic form factor of the neutron, g /equiv G_En/G_Mn , was measured via recoil polarimetry (R.G. Arnold, C.E. Carlson, F. Gross, Phys. Rev. C 23, 363 (1981)) from the quasielastic ²H (/mathop(e)/limitse' /mathop(n)/limits) 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 data reveal that GEn continues to follow the Galster parameterization up to Q² = 1.15 (GeV/c)² and rises 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

[en] We report on precision measurements of the elastic cross section for electron-proton scattering performed in Hall C at Jefferson Lab. The measurements were made at 28 unique kinematic settings covering a range in momentum transfer of 0.4 < Q² < 5.5 (/rm GeV/c)². These measurements represent a significant contribution to the world's cross section data set in the Q² range where a large discrepancy currently exists between the ratio of electric to magnetic proton form factors extracted from previous cross section measurements and that recently measured via polarization transfer in Hall A at Jefferson Lab

[en] The ratio of the proton's electric to magnetic form factor, G_E/G_M, can be extracted in elastic electron-proton scattering by measuring either cross sections, beam-target asymmetry or recoil polarization. Separate determinations of G_E/G_M by cross sections and recoil polarization observables disagree for Q² > 1 (GeV/c)². Measurement by a third technique might uncover an unknown systematic error in either of the previous measurements. The beam-target asymmetry has been measured for elastic electron-proton scattering at Q² = 1.51 (GeV/c)² for target spin orientation aligned perpendicular to the beam momentum direction. This is the largest Q² at which G_E/G_M has been determined by a beam-target asymmetry experiment. The result, μG_E/G_M = 0.884 +/- 0.027 +/- 0.029, is compared to previous world data

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