[en] Results of the Jefferson Lab Hall A quasielastic 3He(e,e'p)pn measurements are presented. These measurements were performed at fixed transferred momentum and energy, q = 1502 MeV/c and omega = 840 MeV, respectively, for missing momenta ± up to 1 GeV/c and missing energies in the continuum region, up to pion threshold; this kinematic coverage is much more extensive than that of any previous experiment. The cross section data are presented along with the effective momentum density distribution and compared to theoretical models

[en] We have studied the quasielastic 3He(e,e'p)d reaction in perpendicular coplanar kinematics, with the energy and momentum transferred by the electron fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e'p)d cross section was measured for missing momenta up to 1000 MeV/c, while the A_TL asymmetry was extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150 MeV/$c$, the measured cross section is described well by calculations that use a variational ground-state wave function of the 3He nucleus derived from a potential that includes three-body forces. For missing momenta from 150 to 750 MeV/c, strong final-state interaction effects are observed. Near 1000 ∼ MeV/c, the experimental cross section is more than an order of magnitude larger than predicted by available theories. The A_TL asymmetry displays characteristic features of broken factorization, and is described reasonably well by available models

[en] We have measured the neutron spin asymmetry A₁ⁿ with high precision at three kinematics in the deep inelastic region at x=0.33, 0.47, and 0.60, and Q²=2.7, 3.5, and 4.8 (GeV/c)², respectively. Our results unambiguously show, for the first time, that A₁ⁿ crosses zero around x=0.47 and becomes significantly positive at x=0.60. Combined with the world proton data, polarized quark distributions were extracted. Our results, in general, agree with relativistic constituent quark models and with perturbative quantum chromodynamics (PQCD) analyses based on the earlier data. However they deviate from PQCD predictions based on hadron helicity conservation

[en] We report on measurements of the neutron spin asymmetries A_1,2ⁿ and polarized structure functions g_1,2ⁿ at three kinematics in the deep inelastic region, with x=0.33, 0.47, and 0.60 and Q²=2.7, 3.5, and 4.8 (GeV/c)², respectively. These measurements were performed using a 5.7 GeV longitudinally polarized electron beam and a polarized ³He target. The results for A₁ⁿ and g₁ⁿ at x=0.33 are consistent with previous world data and, at the two higher-x points, have improved the precision of the world data by about an order of magnitude. The new A₁ⁿ data show a zero crossing around x=0.47 and the value at x=0.60 is significantly positive. These results agree with a next-to-leading-order QCD analysis of previous world data. The trend of data at high x agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (PQCD) assuming hadron helicity conservation. Results for A₂ⁿ and g₂ⁿ have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d₂ⁿ was evaluated and the new result has improved the precision of this quantity by about a factor of 2. When combined with the world proton data, polarized quark distribution functions were extracted from the new g₁ⁿ/F₁ⁿ values based on the quark-parton model. While results for Δu/u agree well with predictions from various models, results for Δd/d disagree with the leading-order PQCD prediction when hadron helicity conservation is imposed

[en] We measured angular distributions of recoil-polarization response functions for neutral pion electroproduction for W=1.23 GeV at Q²=1.0 (GeV/c)², obtaining 14 separated response functions plus 2 Rosenbluth combinations; of these, 12 have been observed for the first time. Dynamical models do not describe quantities governed by imaginary parts of interference products well, indicating the need for adjusting magnitudes and phases for nonresonant amplitudes. We performed a nearly model-independent multipole analysis and obtained values for Re (S₁₊/M₁₊)=-(6.84±0.15)% and Re (E₁₊/M₁₊)=-(2.91±0.19)% that are distinctly different from those from the traditional Legendre analysis based upon M₁₊ dominance and l_π≤1 truncation

[en] We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q²=1.0 (GeV/c)² in 10 bins of 1.17≤W≤1.35 GeV across the Δ resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near the physical mass, W=M_Δ≅1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W>M_Δ. We performed a multipole analysis that adjusts suitable subsets of l_π≤2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent--there is very little sensitivity to the choice of baseline model or truncation scheme. By contrast, truncation errors in the traditional Legendre analysis of N→Δ quadrupole ratios are not negligible. Parabolic fits to the W dependence around M_Δ for the multiple analysis gives values for Re(S₁₊/M₁₊)=(-6.61±0.18)% and Re(E₁₊/M₁₊)=(-2.87±0.19)% for the pπ⁰ channel at W=1.232 GeV and Q²=1.0 (GeV/c)² that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S₀₊/M₁₊)=(+7.1±0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe

[en] We have studied the quasielastic 3He(e,e'p)2H reaction in perpendicular coplanar kinematics, with the energy and the momentum transferred by the electron fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e'p)2H cross section was measured for missing momenta up to 1000 MeV/c, while the ATL asymmetry was extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150 MeV/c, the cross section is described by variational calculations using modern 3He wave functions. For missing momenta from 150 to 750 MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c, the experimental cross section is more than an order of magnitude larger than predicted by available theories. The ATL asymmetry displays characteristic features of broken factorization with a structure that is similar to that generated by available models

[en] A high precision measurement of the transverse spin-dependent asymmetry A_T in ³(rvec H)e((rvec e),e(prime)) quasielastic scattering was performed in Hall A at Jefferson Lab at values of the squared four-momentum transfer, Q², between 0.1 and 0.6 (GeV/c)². A_T is sensitive to the neutron magnetic form factor, G_Mⁿ. Values of G_Mⁿ at Q² = 0.1 and 0.2 (GeV/c)², extracted using Faddeev calculations, were reported previously. Here, we report the extraction of G_Mⁿ for the remaining Q²-values in the range from 0.3 to 0.6 (GeV/c)² using a Plane-Wave Impulse Approximation calculation. The results are in good agreement with recent precision data from experiments using a deuterium target

[en] 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 2x10^-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 10³⁸ 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