W. Korsch

Transverse Asymmetry AT 000 from the Quasielastic 3 He e, e 0 Process and the Neutron Magnetic Form Factor

We have measured the transverse asymmetry A(T) in 3He(e,e()) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%.

The spin dependent momentum distributions of the neutron and proton in 3He

The spin asymmetries in the momentum distributions of the neutron and proton in 3He are obtained from a Faddeev calculation of the ground state. Both two- and three-body configurations are found to be important. Using a PWIA model and measurements of the spin asymmetries in 3&( j?,2p) and 3s( j?,pn) quasielastic scattering at 197 MeV the asymmetries in the momentum distributions are experimentally determined. Good agreement between theory and experiment is found up to initial nucleon momenta of 300 MeV/c.

THE HERMES POLARIZED 3HE INTERNAL GAS TARGET

Abstract The HERMES experiment is investigating the spin structure of the proton and neutron via deep-inelastic scattering of polarized positrons from polarized nuclear targets. The polarized positrons are provided by the HERA positron storage ring at DESY, Hamburg, Germany. The targets are pure internal gas targets. Data acquisition began in 1995, utilizing a polarized 3 He internal gas target to study the spin structure of the neutron. The target gas was polarized using the metastability-exchange optical-pumping technique and then injected into a cryogenically cooled target cell. The target was designed to operate with either longitudinal or transverse directions of polarization. Operating conditions included polarizations of up to 54% and target thicknesses of 1×10 15 nucleons/cm 2 . In this paper the HERMES polarized 3 He internal gas target is described in detail.

Precision measurement of the spin dependent asymmetry in the threshold region of polarized He-3(polarized-e, e-prime)

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

Measurement of the Target-Normal Single-Spin Asymmetry in Quasielastic Scattering from the Reaction (3)He(↑)(e,e').

We report the first measurement of the target single-spin asymmetry, A(y), in quasielastic scattering from the inclusive reaction (3)He(↑)(e,e) on a (3)He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero A(y) can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the substructure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at Q(2)=0.13, 0.46, and 0.97u2009u2009GeV(2). These measurements demonstrate, for the first time, that the (3)He asymmetry is clearly nonzero and negative at the 4σ-9σ level. Using measured proton-to-(3)He cross-section ratios and the effective polarization approximation, neutron asymmetries of -(1-3)% were obtained. The neutron asymmetry at high Q(2) is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at Q(2)=0.97u2009u2009GeV(2) agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.

Measurement of the target-normal single-spin asymmetry in quasielastic scattering from the reaction He3↑(e,e')

We report the first measurement of the target single-spin asymmetry, A(y), in quasielastic scattering from the inclusive reaction (3)He(↑)(e,e) on a (3)He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero A(y) can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the substructure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at Q(2)=0.13, 0.46, and 0.97u2009u2009GeV(2). These measurements demonstrate, for the first time, that the (3)He asymmetry is clearly nonzero and negative at the 4σ-9σ level. Using measured proton-to-(3)He cross-section ratios and the effective polarization approximation, neutron asymmetries of -(1-3)% were obtained. The neutron asymmetry at high Q(2) is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at Q(2)=0.97u2009u2009GeV(2) agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.

Measurements of

We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element d_2 of the neutron (d^n_2) was conducted. The quantity dn_2 represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the ^3He spin structure functions, g_1 and g_2, after nuclear corrections had been applied to these moments. The structure functions were obtained from a measurement of the unpolarized cross section and of double-spin asymmetries in the scattering of a longitudinally polarized electron beam from a transversely and a longitudinally polarized ^3He target. The measurement kinematics included two average Q^2 bins of 3.2u2009u2009GeV^2 and 4.3u2009u2009GeV^2, and Bjorken-x 0.25≤ x ≤0.90 covering the deep inelastic and resonance regions. We have found that d^n_2 is small and negative for ⟨Q^2⟩=3.2u2009u2009GeV^2, and even smaller for ⟨Q^2⟩=4.3u2009u2009GeV^2, consistent with the results of a lattice QCD calculation. The twist-4 matrix element f^n_2 was extracted by combining our measured d^n_2 with the world data on the first moment in x of g^n_1, Γ^n_1. We found f^n_2 to be roughly an order of magnitude larger than dn2. Utilizing the extracted d^n_2 and f^n_2 data, we separated the Lorentz color force into its electric and magnetic components, F^(y,n)_E and F^(y,n)_B, and found them to be equal and opposite in magnitude, in agreement with the predictions from an instanton model but not with those from QCD sum rules. Furthermore, using the measured double-spin asymmetries, we have extracted the virtual photon-nucleon asymmetry on the neutron A^n_1, the structure function ratio g^n_1/F^n_1, and the quark ratios (Δu+Δu)/(u+u) and (Δd+Δd)/(d+d). These results were found to be consistent with deep-inelastic scattering world data and with the prediction of the constituent quark model but at odds with the perturbative quantum chromodynamics predictions at large x.

d_{2}^{n}

We have measured the transverse asymmetry A(T) in 3He(e,e()) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%.

and

We have measured the spin-dependent transverse asymmetry, A_T, in quasi-elastic inclusive electron scattering from polarized 3He with high precision at Q^2 = 0.1 to 0.6 (GeV/c)^2. The neutron magnetic form factor, GMn, was extracted at Q^2 = 0.1 and 0.2 (GeV/c)^2 using a non-relativistic Faddeev calculation that includes both final-state interactions (FSI) and meson-exchange currents (MEC). In addition, GMn was extracted at Q^2 = 0.3 to 0.6 (GeV/c)^2 using a Plane Wave Impulse Approximation calculation. The accuracy of the modeling of FSI and MEC effects was tested and confirmed with a precision measurement of the spin-dependent asymmetry in the breakup threshold region of the 3He(pol)(e(pol),e) reaction. The total relative uncertainty of the extracted GMn data is approximately 3%. Close agreement was found with other recent high-precision GMn data in this Q^2 range.

A_{1}^{n}

Abstract The temperature dependence of the polarization of 3 He atoms in an internal target cell has been studied. Metastable optically pumped polarized 3 He atoms with typical polarization values of 40% were injected into a thin-walled aluminum cell of 40 cm length and a 29.0 × 9.8 mm 2 elliptical cross-section. The cell temperature was varied between 5 and 85 K. The polarization inside the target cell was measured via an asymmetry in the 3 He → (d,p) 4 He reaction at a deuteron energy of 4 MeV. An exponential decrease of the polarization was found for temperatures less than 15 K. For a temperature of ∼6 K a polarization consistent with zero was measured.