G.G. Petratos

Measurements of the Proton and Deuteron Spin Structure Function g2 and Asymmetry A2

We have measured proton and deuteron virtual photon-nucleon asymmetries A2p and A2d and structure functions g2p and g2d over the range 0.03<x<0.8 and 1.3<Q2<10 (GeV/c)2 by inelastically scattering polarized electrons off polarized ammonia targets. Results for A2 are significantly smaller than the positivity limit sqrt(R) for both targets. Within experimental precision, the g2 data are well-described by the twist-2 contribution g2WW. Twist-3 matrix elements have been extracted and are compared to theorectical predictions.

Measurements of the Delta(1232) transition form factor and the ratio sigma(n)/sigma(p) from inelastic electron-proton and electron-deuteron scattering

Measurements of inclusive electron-scattering cross sections using hydrogen and deuterium targets in the region of the Delta(1232) resonance are reported. A global fit to these new data and previous data in the resonance region is also reported for the proton. Transition form factors have been extracted from the proton cross sections for this experiment over the four-momentum transfer squared range 1.64 < Q~2 < 6.75 (GeV/c)~2 and from previous data over the range 2.41 < Q~2 < 9.82 (GeV/c)~2. The results confirm previous reports that the Delta(1232) transition form factor decreases more rapidly with Q~2 than expected from perturbative QCD. The ratio of sigma _n \sigma_p in the \Delta(1232) resonance region has been extracted from the deuteron data for this experiment in the range 1.64 < Q~2 < 3.75 (GeV/c)~2 and for a previous experiment in the range 2.4 < Q~2 < 7.9 (GeV/c)~2. A study has been made of the model dependence of these results. This ratio sigma_n\sigma_p for \Delta(1232) production is slightly less than unity, while sigma_n\sigma_p for the nonresonant cross sections is approximately 0.5, which is consistent with deep inelastic scattering results.

Design and performance of a double-arm 180° spectrometer system for magnetic electron scattering from deuterium

Abstract The design and operation of a double-arm 180° spectrometer system for elastic and inelastic electron scattering from deuterium is described. The system consisted of a chicane of dipole magnets to transport an incident electron beam to a target, an upstream QQQDD spectrometer with a bend angle of 65° to analyze backscattered electrons, a downstream QQQDDDD spectrometer with a bend angle of 66° to detect recoil particles produced at 0°, and a movable beam dump. The large acceptance of the system allowed measurements of the deuteron magnetic elastic B(Q2) and inelastic W1(v, Q2) structure functions at high momentum transfers. The performance is compared to the predictions of a Monte Carlo simulation program.

Two body photodisintegration of the deuteron up to 2.8 GeV

Measurements were performed for the photodisintegration cross section of the deuteron for photon energies from 1.6 GeV to 2.8 GeV and center‐of‐mass angles from 37° to 90°. The measured cross section at θcm=90° are in agreement with the constituent counting rules.

Dynamics of the quasielastic {sup 16}O(e,e{sup '}p) reaction at Q{sup 2}{approx_equal}0.8 (GeV/c){sup 2}

The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed investigation of the ^(16)O(e,e′p) reaction in quasielastic, constant (q,ω) kinematics at Q^2≈0.8(GeV/c)^2, q≈1GeV/c, and ω≈445MeV. Use of a self-calibrating, self-normalizing, thin-film waterfall target enabled a systematically rigorous measurement. Five-fold differential cross-section data for the removal of protons from the 1p-shell have been obtained for 0<p_miss<350MeV/c. Six-fold differential cross-section data for 0<E_miss<120MeV were obtained for 0<p_miss<340MeV/c. These results have been used to extract the ALT asymmetry and the R_L, R_T, R_LT, and R_(L+TT) effective response functions over a large range of E_miss and p_miss. Detailed comparisons of the 1p-shell data with Relativistic Distorted-Wave Impulse Approximation (RDWIA), Relativistic Optical-Model Eikonal Approximation (ROMEA), and Relativistic Multiple-Scattering Glauber Approximation (RMSGA) calculations indicate that two-body currents stemming from meson-exchange currents (MEC) and isobar currents (IC) are not needed to explain the data at this Q^2. Further, dynamical relativistic effects are strongly indicated by the observed structure in ALT at p_miss≈300MeV/c. For 25<E_miss<50MeV and p_miss≈50MeV/c, proton knockout from the 1s1/2-state dominates, and ROMEA calculations do an excellent job of explaining the data. However, as p_miss increases, the single-particle behavior of the reaction is increasingly hidden by more complicated processes, and for 280<p_miss<340MeV/c, ROMEA calculations together with two-body currents stemming from MEC and IC account for the shape and transverse nature of the data, but only about half the magnitude of the measured cross section. For 50<E_miss<120MeV and 145<p_miss<340MeV/c, (e,e′pN) calculations which include the contributions of central and tensor correlations (two-nucleon correlations) together with MEC and IC (two-nucleon currents) account for only about half of the measured cross section. The kinematic consistency of the 1p-shell normalization factors extracted from these data with respect to all available O16(e,e′p) data is also examined in detail. Finally, the Q^2-dependence of the normalization factors is discussed.

Measurements of the proton and deuteron spin structure functionsg1andg2

Measurements are reported of the proton and deuteron spin structure functions g1 at beam energies of 29.1, 16.2, and 9.7 GeV and g2 at a beam energy of 29.1 GeV. The integrals of g1 over x have been evaluated at fixed Q**2 = 3 (GeV/c)**2 using the full data set. The Q**2 dependence of the ratio g1/F1 was studied and found to be small for Q**2>1 (GeV/c)**2. Within experimental precision the g2 data are well-described by the Wandzura-Wilczek twist-2 contribution. Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry A2 was measured and found to be significantly smaller than the positivity limit for both proton and deuteron targets. A2 for the proton is found to be positive and inconsistent with zero. Measurements of g1 in the resonance region show strong variations with x and Q**2, consistent with resonant amplitudes extracted from unpolarized data. These data allow us to study the Q**2 dependence of the first moments of g1 below the scaling region.

Inclusive electron scattering from nuclei at {ital x}{approx_equal}1

The inclusive A(e, e{prime}) cross section for x {approx_equal} 1 was measured on {sup 2}H, C, Fe, and Au for momentum transfers Q{sup 2} from 1-7 (GeV/c){sup 2}. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit {zeta}-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.

Inclusive electron scattering from nuclei atx≃1

The inclusive A(e, e{prime}) cross section for x {approx_equal} 1 was measured on {sup 2}H, C, Fe, and Au for momentum transfers Q{sup 2} from 1-7 (GeV/c){sup 2}. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit {zeta}-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.

Transverse inelastic electron scattering from the deuteron at high momentum transfers

Cross sections for 180° inelastic electron scattering from the deuteron were measured from the break‐up threshold to beyond the quasielastic peak for incident beam energies between 0.7 and 1.3 GeV, corresponding to 0.75≤Q2≤2.75 (GeV/c)2. The data are in reasonable agreement with nonrelativistic models that include final‐state interactions are meson exchange currents.

A-dependence of deep-inelastic electron scattering from nuclei

The deep inelastic electron scattering cross sections per nucleon sigma/sub A/ for d, He, Be, C, Al, Ca, Fe, Ag, and Au were measured in the kinematic range 0.09 less than or equal to x less than or equal to 0.9 and 2 less than or equal to Q/sup 2/ less than or equal to 15 (GEV/c)/sup 2/ using electrons with energies ranging from 8 to 24.5 GeV. The ratio sigma/sub A//sigma/sub d/ is consistent with unity in the range 0.1 < x < 0.3. For 0.3 < x < 0.8, the ratio decreases logarithmically with atomic weight A, or linearly with average nuclear density. No Q/sup 2/ dependence in the ratio was observed over the kinematic range of the data. 12 references.