[en] The 2H(e,e'p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility (JLab) in quasielastic kinematics (x=0.96) at a four-momentum transfer squared, Q²=0.67 (GeV/c)². The experiment was performed in fixed electron kinematics for recoil momenta from zero to 550 MeV/c. Though the measured cross section deviates by 1-2 sigma from a state-of-the-art calculation at low recoil momenta, it agrees at high recoil momenta where final state interactions (FSI) are predicted to be large

[en] The authors propose a measurement of the Deep Virtual Compton Scattering process (DVCS) ep → epγ in Hall A at Jefferson Lab with a 6 GeV beam. The authors are able to explore the onset of Q² scaling, by measuring a beam helicity asymmetry for Q² ranging from 1.5 to 2.5 GeV² at x_B ∼ 0.35. At this kinematics, the asymmetry is dominated by the DVCS Bethe-Heitler (BH) interference, which is proportional to the imaginary part of the DVCS amplitude amplified by the full magnitude of the BH amplitude. The imaginary part of the DVCS amplitude is expected to scale early. Indeed, the imaginary part of the forward Compton amplitude measured in deep inelastic scattering (via the optical theorem) scales at Q² as low as 1 GeV². If the scaling regime is reached, they make an 8% measurement of the skewed parton distributions (SPD) contributing to the DVCS amplitude. Also, this experiment allows them to separately estimate the size of the higher-twist effects, since they are only suppressed by an additional factor 1/Q compared to the leading-twist term, and have a different angular dependence. They use a polarized electron beam and detect the scattered electron in the HRSe, the real photon in an electromagnetic calorimeter (under construction) and the recoil proton in a shielded scintillator array (to be constructed). This allows them to determine the difference in cross-sections for electrons of opposite helicities. This observable is directly linked to the SPD's. The authors estimate that 25 days of beam (600 hours) are needed to achieve this goal

[en] The recoil proton polarization was measured in the d(epol,e' ppol)n reaction in Hall A of the Thomas Jefferson National Accelerator Facility (JLab). The electron kinematics were centered on the quasielastic peak (x_Bj ∼ 1) and included three values of the squared four-momentum transfer, Q²=0.43, 1.00 and 1.61 (GeV/c)². For Q²=0.43 and 1.61 (GeV/c)², the missing momentum, p_m, was centered at zero while for Q²=1.00 (GeV/c)² two values of p_m were chosen: 0 and 174 MeV/c. At low p_m, the Q² dependence of the longitudinal polarization, P_z', is not well described by a state-of-the-art calculation. Further, at higher p_m, a 3.5 sigma discrepancy was observed in the transverse polarization, P_x'. Understanding the origin of these discrepancies is important in order to confidently extract the neutron electric form factor from the analogous d(epol,e' npol)p experiment

[en] We present a measurement of the induced proton polarization P_n in π⁰ electroproduction on the proton around the Δ resonance. The measurement was made at a central invariant mass and a squared four-momentum transfer of W = 1231 MeV and Q² = 0.126 GeV²/c², respectively. We measured a large induced polarization, P_n = -0.397 ± 0.055 ± 0.009. The data suggest that the scalar background is larger than expected from a recent effective Hamiltonian model

[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 present the first measurements of (rvec e)p → epγ cross section in the deep virtual Compton scattering (DVCS) regime and the valence quark region (x_Bj = 0.36). From JLab E00-110, we extract the imaginary part of the Bethe-Heitler (BH)--DVCS interference terms, to order twist-3 for Q² = 1.5, 1.9, and 2.3 GeV², and the real part of the BH-DVCS interference terms at Q²2 = 2.3 GeV². We present the first model-independent measurement of linear combinations of generalized parton distributions (GPDs) and GPD integrals up to twist-3 approximation. The validity of this approximation is strongly supported by the absence of Q²-variation of the extracted terms--thereby constraining the size of higher twist contributions to our observables

[en] We present measurements of the ratio of the proton elastic electromagnetic form factors, μpGEp/GMp. The Jefferson Lab Hall A Focal Plane Polarimeter was used to determine the longitudinal and transverse components of the recoil proton polarization in ep elastic scattering; the ratio of these polarization components is proportional to the ratio of the two form factors. These data reproduce the observation of Jones et al. [Phys. Rev. Lett. 84, 1398 (2000)], that the form factor ratio decreases significantly from unity above Q2 = 1 GeV2