[en] A precise measurement of the p((rvec e), e'(rvec p))π⁰ reaction at the Δ(1232) resonance with Q² = 0.9, 1.1(GeV/c)² was conducted in experimental Hall A at the Jefferson Lab. The angular distributions of the coincidence cross section and recoil polarization in the pion electro-production process were used for the extraction of both the unpolarized and polarized response functions. By including the recoil polarization observables, a large number of response functions are obtained for a model-independent multipole analysis to extract both the dominant and small amplitudes in the p(e, e'p)π⁰ reaction, which are important for understanding nucleon structure and the N→Δ transition mechanism. This thesis describes the experimental setup and the details of the absolute cross section analysis. A data-defined R-Function method was developed for the precise analysis of the small acceptance of the Hall A spectrometer. A simple and efficient analysis procedure for absolute cross section extraction with extensive use of simulation was designed and used. The extracted cross section results were parameterized for the extraction of polarized response functions from recoil polarizations. The cross section results and preliminary polarization and multipole results are presented. The N → Δ quadrupole transition ratios R_EM and R_SM extracted from the differential cross sections are compared with those from the preliminary multipole analysis results

[en] For the first time the simultaneous separation of many RFs with a recoil polarization technique has been applied for measurements covering a large fraction of the phase space, even if for a single Q², W setting. The technique has been proven valid and 14 RFs can be individually extracted within the same set of measurements with the additional information coming from two combinations of the other 4. Then, the technical aim has been already achieved. Multipole decomposition, the most model independent analysis that can be made, is still to be done. Its result should give the physical information about the size of the small resonant and non resonant contributions. This is the physics aim of the experiment and will define the sensitivity of the technique. From this result one will infer the suitability to perform measurements at other Q², W settings or/and for other reactions. The technique is applicable to leptoproduction experiments in higher energy regimes provided that models, supposed to describe hadronic systems in that regimes, offer the opportunity to test their predictions in terms of RFs

[en] The generalized forward spin polarizabilities γ₀ and (delta)_LT of the neutron have been extracted for the first time in a Q² range from 0.1 to 0.9 GeV². Since γ₀ is sensitive to nucleon resonances and (delta)_LT is insensitive to the Δ resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on (delta)_LT show significant disagreement with Chiral Perturbation Theory calculations, while the data for γ₀ at low Q² are in good agreement with a next-to-lead order Relativistic Baryon Chiral Perturbation theory calculation. The data show good agreement with the phenomenological MAID model

[en] We present measurements of the recoil proton polarization for the ¹H(gamma-vector,p-vector)pi⁰ reaction for theta_c.m.^pi = 60^o-135^o and for photon energies up to 4.1 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. Various theoretical models are compared with the results. No evidence for hadron helicity conservation is observed. Models that employ factorization are not favored. It appears from the strong angular dependence of the induced polarization at photon energies of 2.5 and 3.1 GeV that a relatively high spin resonance or background amplitude might exist in this energy region

[en] We present measurements of the recoil proton polarization for the d(polarized y, polarized p)n reaction at thetac.m. = 90 degrees for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization py vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(y,p)n cross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime

[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 .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 two. 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 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

[en] We have measured the transverse asymmetry from inclusive scattering of longitudinally polarized electrons from polarized ³He nuclei at quasi-elastic kinematics in Hall A at Jefferson Lab with high statistical and systematic precision. The neutron magnetic form factor was extracted based on Faddeev calculations with an experimental uncertainty of less than 2%

[en] We have measured the transverse asymmetry A_T' in the quasi-elastic ³/rvec He/(/rvec e/,e') process with high precision at Q²-values from 0.1 to 0.6 (GeV/c)². The neutron magnetic form factor G_Mⁿ was extracted at Q²-values of 0.1 and 0.2 (GeV/c)² using a non-relativistic Faddeev calculation which includes both final-state interactions (FSI) and meson-exchange currents (MEC). Theoretical uncertainties due to the FSI and MEC effects were constrained with a precision measurement of the spin-dependent asymmetry in the threshold region of ³/rvec He/(/rvec e/,e'). We also extracted the neutron magnetic form factor G_Mⁿ at Q²-values of 0.3 to 0.6 (GeV/c)² based on Plane Wave Impulse Approximation calculations

[en] We present the first precision measurement of the spin-dependent asymmetry in the threshold region of ³He(e,e(prime)) at Q²-values of 0.1 and 0.2 (GeV/c)². The agreement between the data and non-relativistic Faddeev calculations which include both final-state interactions (FSI) and meson-exchange currents (MEC) effects is very good at Q² = 0.1 (GeV/c)², while a small discrepancy at Q² = 0.2 (GeV/c)² is observed