Showing papers by "Timothy B. Smith published in 1998"

Measurements of the Proton and Deuteron Spin Structure Functions g1 and g2

Abstract: Measurements are reported of the proton and deuteron spin structure functions ${g}_{1}^{p}$ and ${g}_{1}^{d}$ at beam energies of 29.1, 16.2, and 9.7 GeV, and ${g}_{2}^{p}$ and ${g}_{2}^{d}$ at a beam energy of 29.1 GeV. The integrals ${\ensuremath{\Gamma}}_{p}={\ensuremath{\int}}_{0}^{1}{g}_{1}^{p}{(x,Q}^{2})dx$ and ${\ensuremath{\Gamma}}_{d}={\ensuremath{\int}}_{0}^{1}{g}_{1}^{d}{(x,Q}^{2})dx$ were evaluated at fixed ${Q}^{2}=3(\mathrm{GeV}{/c)}^{2}$ using the full data set to yield ${\ensuremath{\Gamma}}_{p}=0.132\ifmmode\pm\else\textpm\fi{}0.003(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.009(\mathrm{syst})$ and ${\ensuremath{\Gamma}}_{d}=0.047\ifmmode\pm\else\textpm\fi{}0.003\ifmmode\pm\else\textpm\fi{}0.006.$ The ${Q}^{2}$ dependence of the ratio ${g}_{1}{/F}_{1}$ was studied and found to be small for ${Q}^{2}g1(\mathrm{GeV}{/c)}^{2}.$ Within experimental precision the ${g}_{2}$ data are well described by the twist-2 contribution, ${g}_{2}^{\mathrm{WW}}.$ Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry ${A}_{2}$ was measured and found to be significantly smaller than the positivity limit $\sqrt{R}$ for both proton and deuteron targets. ${A}_{2}^{p}$ is found to be positive and inconsistent with zero. Measurements of ${g}_{1}$ 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 integrals ${\ensuremath{\Gamma}}_{p}$ and ${\ensuremath{\Gamma}}_{n}$ below the scaling region.

Observation of Forward Shocks and Stagnated Ejecta Driven by High-Energy-Density Plasma Flow

Abstract: Laboratory studies of hydrodynamic effects driven by a flowing, expanding plasma of high-energy density and high Mach number are reported. The flowing plasma is the ejecta from matter accelerated and heated by an ablative shock. X-ray backlighting diagnoses the structure produced when this plasma impacts low-density foam. We observe the forward shock driven into the foam and the stagnated ejecta which drives a reverse shock into the flow.

Toward precision polarimetry of dense polarized 3He targets

Abstract: We describe several new measurement and analysis techniques used to determine the polarization of the 3He target in a recently completed measurement of the neutron spin structure function g 1n at SLAC (E-154). The polarization was determined using two independent methods. The first method used a standard technique of Adiabatic Fast Passage, calibrated by a measurement of Boltzmann polarization in a sample of water. We describe several systematic effects affecting this calibration procedure. The second method used a shift of the Rb Zeeman resonance frequency due to the polarization of 3He. Implementation and calibration of this technique are discussed in detail. Finally, the density of 3He in the cell was measured using two independent methods, one of them based on the pressure broadening of Rb D1 and D2 lines due to 3He.

Recent advances in spin-exchange pumped polarized 3He target technology

Abstract: We have produced long lifetime 3 He spin-exchange cells from Corning 7056 glass. The lifetimes of single cells have approached the 3 He 3 He bulk-limited lifetime (250 h at a density of 8 × 10 19 cm −3 , (3 amagats)). Corning 7056 glass has the advantage of being a much easier glass for the glassblower to work, allowing for more complex cell designs. In our experiments at Michigan and at SLAC, we have implemented laser diode arrays for spin-exchange optical pumping. In particular, for experiment E154 at SLAC, we achieved high polarizations in high-density 3 He targets using laser diode arrays.

Spin exchange pumped 3He targets: progress and prospects

Abstract: Polarized 3He has been used as a spin filter for neutron polarization, as a target to probe neutron structure, and in combination with 129Xe for precision measurement of fundamental physics. Spin exchange pumped masers of one and two species have run for weeks and allow CW measurement with precision trending as steeply as τ −3 2 . At SLAC, a program of experiments has studied the neutron spin-dependent structure function in deep inelastic scattering, exploiting the large neutron polarization in a polarized 3He target. Data from the most recent experiment provide new precise data with Bjorken x down to 0.014. Among the conclusions is the need to consider Q2 dependence in interpretation of the data and determination of sum rules (sums over the full range in x).