Metastable helium molecules as tracers in superfluid liquid 4^{4}He

Metastable helium molecules generated in a discharge near a sharp tungsten tip operated in either pulsed mode or continuous field-emission mode in superfluid liquid $^{4}$He are imaged using a laser-induced-fluorescence technique. By pulsing the tip, a small cloud of He$_{2}^{*}$ molecules is produced. At 2.0 K, the molecules in the liquid follow the motion of the normal fluid. We can determine the normal-fluid velocity in a heat-induced counterflow by tracing the position of a single molecule cloud. As we run the tip in continuous field-emission mode, a normal-fluid jet from the tip is generated and molecules are entrained in the jet. A focused 910 nm pump laser pulse is used to drive a small group of molecules to the vibrational $a(1)$ state. Subsequent imaging of the tagged $a(1)$ molecules with an expanded 925 nm probe laser pulse allows us to measure the velocity of the normal fluid. The techniques we developed demonstrate for the first time the ability to trace the normal-fluid component in superfluid helium using angstrom-sized particles.Comment: 4 pages, 7 figures. Submitted to Phys. Rev. Let

A 83Krm Source for Use in Low-background Liquid Xenon Time Projection Chambers

We report the testing of a charcoal-based Kr-83m source for use in calibrating a low background two-phase liquid xenon detector. Kr-83m atoms produced through the decay of Rb-83 are introduced into a xenon detector by flowing xenon gas past the Rb-83 source. 9.4 keV and 32.1 keV transitions from decaying 83Krm nuclei are detected through liquid xenon scintillation and ionization. The characteristics of the Kr-83m source are analyzed and shown to be appropriate for a low background liquid xenon detector. Introduction of Kr-83m allows for quick, periodic calibration of low background noble liquid detectors at low energy.Comment: Updated to version submitted to JINS

Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields

The drift and diffusion of a cloud of ions in a fluid are distorted by an inhomogeneous electric field. If the electric field carries the center of the distribution in a straight line and the field configuration is suitably symmetric, the distortion can be calculated analytically. We examine the specific examples of fields with cylindrical and spherical symmetry in detail assuming the ion distributions to be of a generally Gaussian form. The effects of differing diffusion coefficients in the transverse and longitudinal directions are included

Calibration of liquid argon and neon detectors with 83Krm^{83}Kr^m

We report results from tests of $^{83}$Kr$^{\mathrm{m}}$, as a calibration source in liquid argon and liquid neon. $^{83}$Kr$^{\mathrm{m}}$ atoms are produced in the decay of $^{83}$Rb, and a clear $^{83}$Kr$^{\mathrm{m}}$ scintillation peak at 41.5 keV appears in both liquids when filling our detector through a piece of zeolite coated with $^{83}$Rb. Based on this scintillation peak, we observe 6.0 photoelectrons/keV in liquid argon with a resolution of 6% ($\sigma$/E) and 3.0 photoelectrons/keV in liquid neon with a resolution of 19% ($\sigma$/E). The observed peak intensity subsequently decays with the $^{83}$Kr$^{\mathrm{m}}$ half-life after stopping the fill, and we find evidence that the spatial location of $^{83}$Kr$^{\mathrm{m}}$ atoms in the chamber can be resolved. $^{83}$Kr$^{\mathrm{m}}$ will be a useful calibration source for liquid argon and neon dark matter and solar neutrino detectors.Comment: 7 pages, 12 figure

Dynamics of Phase Transitions: The 3D 3-state Potts model

In studies of the QCD deconfining phase transition or cross-over by means of heavy ion experiments, one ought to be concerned about non-equilibrium effects due to heating and cooling of the system. In this paper we extend our previous study of Glauber dynamics of 2D Potts models to the 3D 3-state Potts model, which serves as an effective model for some QCD properties. We investigate the linear theory of spinodal decomposition in some detail. It describes the early time evolution of the 3D model under a quench from the disordered into the ordered phase well, but fails in 2D. Further, the quench leads to competing vacuum domains, which are difficult to equilibrate, even in the presence of a small external magnetic field. From our hysteresis study we find, as before, a dynamics dominated by spinodal decomposition. There is evidence that some effects survive in the case of a cross-over. But the infinite volume extrapolation is difficult to control, even with lattices as large as $120^3$.Comment: 12 pages; added references, corrected typo

Azimuthal Correlation in Lepton-Hadron Scattering via Charged Weak-Current Processes

We consider the azimuthal correlation of the final-state particles in charged weak-current processes. This correlation provides a test of perturbative quantum chromodynamics. The azimuthal asymmetry is large in the semi-inclusive processes in which we identify a final-state hadron, say, a charged pion compared to that in the inclusive processes in which we do not identify final-state particles and use only the calorimetric information. In semi-inclusive processes the azimuthal asymmetry is more conspicuous when the incident lepton is an antineutrino or a positron than when the incident lepton is a neutrino or an electron. We analyze all the possible charged weak-current processes and study the quantitative aspects of each process. We also compare this result to the ep scattering with a photon exchange.Comment: 25 pages, 2 Postscript figures, uses RevTeX, fixes.st

Glauber dynamics of phase transitions: SU(3) lattice gauge theory

Motivated by questions about the QCD deconfining phase transition, we studied in two previous papers Model A (Glauber) dynamics of 2D and 3D Potts models, focusing on structure factor evolution under heating (heating in the gauge theory notation, i.e., cooling of the spin systems). In the present paper we set for 3D Potts models (Ising and 3-state) the scale of the dynamical effects by comparing to equilibrium results at first and second order phase transition temperatures, obtained by re-weighting from a multicanonical ensemble. Our finding is that the dynamics entirely overwhelms the critical and non-critical equilibrium effects. In the second half of the paper we extend our results by investigating the Glauber dynamics of pure SU(3) lattice gauge on $N_{\tau} N_{\sigma}^3$ lattices directly under heating quenches from the confined into the deconfined regime. The exponential growth factors of the initial response are calculated, which give Debye screening mass estimates. The quench leads to competing vacuum domains of distinct $Z_3$ triality, which delay equilibration of pure gauge theory forever, while their role in full QCD remains a subtle question. As in spin systems we find for pure SU(3) gauge theory a dynamical growth of structure factors, reaching maxima which scale approximately with the volume of the system, before settling down to equilibrium. Their influence on various observables is studied and different lattice sizes are simulated to illustrate an approach to a finite volume continuum limit. Strong correlations are found during the dynamical process, but not in the deconfined phase at equilibrium.Comment: 12 pages, 18 figure

Identifying and Indexing Icosahedral Quasicrystals from Powder Diffraction Patterns

We present a scheme to identify quasicrystals based on powder diffraction data and to provide a standardized indexing. We apply our scheme to a large catalog of powder diffraction patterns, including natural minerals, to look for new quasicrystals. Based on our tests, we have found promising candidates worthy of further exploration.Comment: 4 pages, 1 figur