38,456 research outputs found
Parity-violating electron scattering and nucleon structure
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 He in superfluid He
We calculate the effect of a heat current on transporting He dissolved in
superfluid He 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)
He down a long pipe. In the regime of He concentrations and temperatures 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 He first
viscosity. On the other hand, the phonon wind drives the He out of local
equilibrium via phonon-He scattering. For temperatures below K, both
the phonon and He 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 He
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 He atoms is determined by the
time dependent He diffusion equation, which describes the competition
between advection by the phonon wind and He diffusion. As a consequence of
the thermal diffusivity being small compared with the He diffusivity, the
scale height of the final He distribution is much smaller than that of the
temperature gradient. We present exact solutions of the time dependent
temperature and He 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 He in superfluid He
Motivated by a proposed experimental search for the electric dipole moment of
the neutron (nEDM) utilizing neutron-He capture in a dilute solution of
He in superfluid He, we derive the transport properties of dilute
solutions in the regime where the He are classically distributed and rapid
He-He scatterings keep the He in equilibrium. Our microscopic
framework takes into account phonon-phonon, phonon-He, and He-He
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 He in Superfluid He
We report microscopic calculations of the thermal conductivity, diffusion
constant and thermal diffusion constant for classical solutions of He in
superfluid He at temperatures T \la 0.6~K, where phonons are the dominant
excitations of the He. We focus on solutions with He 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
He-phonon scattering, which is crucial for determining the He
distribution function in transport. We use the fact that the relative changes
in the energy and momentum of a He atom in a collision with a phonon are
small to derive a Fokker-Planck equation for the He 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
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 stars, and
the starburst is 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
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
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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