38,456 research outputs found

    Parity-violating electron scattering and nucleon structure

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    The measurement of parity violation in the helicity dependence of electron-nucleon scattering provides unique information about the basic quark structure of the nucleons. This review presents the general formalism of parity-violating electron scattering, with emphasis on elastic electron-nucleon scattering. The physics issues addressed by such experiments are discussed, and the major goals of the presently envisioned experimental program are identified. Results from a recent series of experiments are summarized and the future prospects of this program are discussed

    Transport in ultradilute solutions of 3^3He in superfluid 4^4He

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    We calculate the effect of a heat current on transporting 3^3He dissolved in superfluid 4^4He at ultralow concentration, as will be utilized in a proposed experimental search for the electric dipole moment of the neutron (nEDM). In this experiment, a phonon wind will generated to drive (partly depolarized) 3^3He down a long pipe. In the regime of 3^3He concentrations <~10−9\tilde < 10^{-9} and temperatures ∼0.5\sim 0.5 K, the phonons comprising the heat current are kept in a flowing local equilibrium by small angle phonon-phonon scattering, while they transfer momentum to the walls via the 4^4He first viscosity. On the other hand, the phonon wind drives the 3^3He out of local equilibrium via phonon-3^3He scattering. For temperatures below 0.50.5 K, both the phonon and 3^3He mean free paths can reach the centimeter scale, and we calculate the effects on the transport coefficients. We derive the relevant transport coefficients, the phonon thermal conductivity and the 3^3He diffusion constants from the Boltzmann equation. We calculate the effect of scattering from the walls of the pipe and show that it may be characterized by the average distance from points inside the pipe to the walls. The temporal evolution of the spatial distribution of the 3^3He atoms is determined by the time dependent 3^3He diffusion equation, which describes the competition between advection by the phonon wind and 3^3He diffusion. As a consequence of the thermal diffusivity being small compared with the 3^3He diffusivity, the scale height of the final 3^3He distribution is much smaller than that of the temperature gradient. We present exact solutions of the time dependent temperature and 3^3He distributions in terms of a complete set of normal modes.Comment: NORDITA PREPRINT 2015-37, 9 pages, 6 figure

    Transport in very dilute solutions of 3^3He in superfluid 4^4 He

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    Motivated by a proposed experimental search for the electric dipole moment of the neutron (nEDM) utilizing neutron-3^3He capture in a dilute solution of 3^3He in superfluid 4^4 He, we derive the transport properties of dilute solutions in the regime where the 3^3He are classically distributed and rapid 3^3He-3^3He scatterings keep the 3^3He in equilibrium. Our microscopic framework takes into account phonon-phonon, phonon-3^3He, and 3^3He-3^3He scatterings. We then apply these calculations to measurements by Rosenbaum et al. [J.Low Temp.Phys. {\bf 16}, 131 (1974)] and by Lamoreaux et al. [Europhys.Lett. {\bf 58}, 718 (2002)] of dilute solutions in the presence of a heat flow. We find satisfactory agreement of theory with the data, serving to confirm our understanding of the microscopics of the helium in the future nEDM experiment.Comment: 10 pages, 5 figures, v

    Low Temperature Transport Properties of Very Dilute Classical Solutions of 3^3He in Superfluid 4^4He

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    We report microscopic calculations of the thermal conductivity, diffusion constant and thermal diffusion constant for classical solutions of 3^3He in superfluid 4^4He at temperatures T \la 0.6~K, where phonons are the dominant excitations of the 4^4He. We focus on solutions with 3^3He concentrations \la \,10^{-3}, for which the main scattering mechanisms are phonon-phonon scattering via 3-phonon Landau and Beliaev processes, which maintain the phonons in a drifting equilibrium distribution, and the slower process of 3^3He-phonon scattering, which is crucial for determining the 3^3He distribution function in transport. We use the fact that the relative changes in the energy and momentum of a 3^3He atom in a collision with a phonon are small to derive a Fokker-Planck equation for the 3^3He distribution function, which we show has an analytical solution in terms of Sonine polynomials. We also calculate the corrections to the Fokker-Planck results for the transport coefficients.Comment: 29 pages, 2 figure

    The Infrared Nucleus of the Wolf-Rayet Galaxy Henize 2-10

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    We have obtained near-infrared images and mid-infrared spectra of the starburst core of the dwarf Wolf-Rayet galaxy He 2-10. We find that the infrared continuum and emission lines are concentrated in a flattened ellipse 3-4'' or 150 pc across which may show where a recent accretion event has triggered intense star formation. The ionizing radiation from this cluster has an effective temperature of 40,000 K, corresponding to 30M⊙30M_\odot stars, and the starburst is 0.5−1.5×1070.5-1.5 \times 10^7 years old.Comment: 17 pages Latex, 7 postscript figures, 1 postscript table, accepted to A

    Experimental determination of cosmic ray charged particle intensity profiles in the atmosphere

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    Absolute cosmic-ray free air ionization and charged particle fluxes and dose rates throughout the atmosphere were measured on a series of balloon flights that commenced in 1968. Argon-filled ionization chambers equipped with solid-state electrometers, with different gas pressures and steel wall thicknesses, and a pair of aluminum-wall Gm counters have provided the basic data. These data are supplemented by measurements with air-filled and tissue equivalent ionization chambers and a scintillation spectrometer. Laboratory experiments together with analyses of the theoretical aspects of the detector responses to cosmic radiation indicate that these profiles can be determined to an overall accuracy of + or - 5 percent

    Parity-Violating Electron Scattering and Neucleon Structure

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    The measurement of parity violation in the helicity dependence of electron-nucleon scattering provides unique information about the basic quark structure of the nucleons. In this review, the general formalism of parity-violating electron scattering is presented, with emphasis on elastic electron-nucleon scattering. The physics issues addressed by such experiments is discussed, and the major goals of the presently envisioned experimental program are identified. %General aspects of the experimental technique are reviewed and A summary of results from a recent series of experiments is presented and the future prospects of this program are also discussed.Comment: 45 pages, 9 figure
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