Steven Williamson

Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasielastic Electron-Deuteron Scattering

We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasielastic scattering on the deuteron, at backward angles (lab scattering angle of 108°) for Q² = 0.22 GeV²/c² and 0.63 GeV²/c² at beam energies of 362 and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single-photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (πN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasistatic deuterium approximation, and is also in agreement with theory.

An Apparatus for Studying Electrical Breakdown in Liquid Helium at 0.4 K and Testing Electrode Materials for the Neutron Electric Dipole Moment Experiment at the Spallation Neutron Source

testing electrode materials for the SNS nEDM experiment T. M. Ito, a) J. C. Ramsey, W. Yao, D. H. Beck, V. Cianciolo, S. M. Clayton, C. Crawford, S. A. Currie, B. W. Filippone, W. C. Griffith, M. Makela, R. Schmid, G. M. Seidel, Z. Tang, D. Wagner, W. Wei, and S. E. Williamson Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Loomis Laboratory of Physics, University of Illinois, Urbana, Illinois 61801, USA Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California, 91125, USA Department of Physics, Brown University, Providence, Rhode Island, 02912, USAWe have constructed an apparatus to study DC electrical breakdown in liquid helium at temperatures as low as 0.4 K and at pressures between the saturated vapor pressure and ∼600 Torr. The apparatus can house a set of electrodes that are 12 cm in diameter with a gap of 1-2 cm between them, and a potential up to ±50 kV can be applied to each electrode. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes 12 cm in diameter for a wide range of pressures at 0.4 K. We also measured the current between two electrodes. Our initial results, I < 1 pA at 45 kV, correspond to a lower bound on the effective volume resistivity of liquid helium of ρV > 5 × 10(18) Ω cm. This lower bound is 5 times larger than the bound previously measured. We report the design, construction, and operational experience of the apparatus, as well as initial results.