301 research outputs found
Dynamics of Complex Quantum Systems: Dissipation and Kinetic Equations
We present a microscopic approach to quantum dissipation and sketch the
derivation of the kinetic equation describing the evolution of a simple quantum
system in interaction with a complex quantum system. A typical quantum complex
system is modeled by means of parametric banded random matrices coupled to the
subsystem of interest. We do not assume the weak coupling limit and allow for
an independent dynamics of the ``reservoir''. We discuss the reasons for having
a new theoretical approach and the new elements introduced by us. The present
approach incorporates known limits and previous results, but at the same time
includes new cases, previously never derived on a microscopic level. We briefly
discuss the kinetic equation and its solution for a particle in the absence of
an external field.Comment: 7 pages, Elsevier style file espcrc2.st
Comparison of CDMS [100] and [111] oriented germanium detectors
The Cryogenic Dark Matter Search (CDMS) utilizes large mass, 3" diameter
1" thick target masses as particle detectors. The target is
instrumented with both phonon and ionization sensors and comparison of energy
in each channel provides event-by-event classification of electron and nuclear
recoils. Fiducial volume is determined by the ability to obtain good phonon and
ionization signal at a particular location. Due to electronic band structure in
germanium, electron mass is described by an anisotropic tensor with heavy mass
aligned along the symmetry axis defined by the [111] Miller index (L valley),
resulting in large lateral component to the transport. The spatial distribution
of electrons varies significantly for detectors which have their longitudinal
axis orientations described by either the [100] or [111] Miller indices.
Electric fields with large fringing component at high detector radius also
affect the spatial distribution of electrons and holes. Both effects are
studied in a 3 dimensional Monte Carlo and the impact on fiducial volume is
discussed.Comment: Low Temperature Detector 14 conference proceedings to be published in
the Journal of Low Temperature Physic
Effect of Airborne Hydrocarbons on the Wettability of Phase Change Nanoparticle Decorated Surfaces
We present here a detailed study of the wettability of surfaces nanostructured with amorphous and crystalline nanoparticles (NPs) derived from the phase-change material Ge2Sb2Te5 (GST). Particular attention was devoted to the effect of airborne surface hydrocarbons on surface wetting. Our analysis illustrates that a reversible hydrophilic-hydrophobic wettability switch is revealed by combined ultraviolet-ozone (UV-O-3) treatments and exposure to hydrocarbon atmospheres. Indeed, the as prepared surfaces exhibited a hydrophilic state after thermal annealing or UV-O-3 treatment which can partially remove hydrocarbon contaminants, while a hydrophobic state was realized after exposure to hydrocarbon atmosphere. Using high-angle annular dark-field scanning transmission electron microscopy for the specially designed GST NP decorated graphene substrates, a network of hydrocarbon connecting GST NPs was observed. Our findings indicate that airborne hydrocarbons can significantly enhance the hydrophobicity of nanostructured surfaces. Finally, the experiments reveal that previously defined hydrophilic materials can be used for the design of hydrophobic surfaces even if the meniscus is highly adhered to a solid surface, which is in agreement with our qualitative model involving the contribution of the nanomeniscus formed between the substrate and a decorating NP
Validation of Phonon Physics in the CDMS Detector Monte Carlo
The SuperCDMS collaboration is a dark matter search effort aimed at detecting
the scattering of WIMP dark matter from nuclei in cryogenic germanium targets.
The CDMS Detector Monte Carlo (CDMS-DMC) is a simulation tool aimed at
achieving a deeper understanding of the performance of the SuperCDMS detectors
and aiding the dark matter search analysis. We present results from validation
of the phonon physics described in the CDMS-DMC and outline work towards
utilizing it in future WIMP search analyses.Comment: 6 Pages, 5 Figures, Proceedings of Low Temperature Detectors 14
Conferenc
Derivation and assessment of strong coupling core-particle model from the Kerman-Klein-D\"onau-Frauendorf theory
We review briefly the fundamental equations of a semi-microscopic
core-particle coupling method that makes no reference to an intrinsic system of
coordinates. We then demonstrate how an intrinsic system can be introduced in
the strong coupling limit so as to yield a completely equivalent formulation.
It is emphasized that the conventional core-particle coupling calculation
introduces a further approximation that avoids what has hitherto been the most
time-consuming feature of the full theory, and that this approximation can be
introduced either in the intrinsic system, the usual case, or in the laboratory
system, our preference. A new algorithm is described for the full theory that
largely removes the difference in complexity between the two types of
calculation. Comparison of the full and approximate theories for some
representative cases provides a basis for the assessment of the accuracy of the
traditional approach. We find that for well-deformed nuclei, e.g. 157Gd and
157Tb, the core-coupling method and the full theory give similar results.Comment: revtex, 3 figures(postscript), submitted to Phys.Rev.
Preliminary Limits on the WIMP-Nucleon Cross Section from the Cryogenic Dark Matter Search (CDMS)
We are conducting an experiment to search for WIMPs, or weakly-interacting
massive particles, in the galactic halo using terrestrial detectors. This
generic class of hypothetical particles, whose properties are similar to those
predicted by extensions of the standard model of particle physics, could
comprise the cold component of non-baryonic dark matter. We describe our
experiment, which is based on cooled germanium and silicon detectors in a
shielded low-background cryostat. The detectors achieve a high degree of
background rejection through the simultaneous measurement of the energy in
phonons and ionization. Using exposures on the order of one kilogram-day from
initial runs of our experiment, we have achieved (preliminary) upper limits on
the WIMP-nucleon cross section that are comparable to much longer runs of other
experiments.Comment: 5 LaTex pages, 5 eps figs, epsf.sty, espcrc2dsa2.sty. Proceedings of
TAUP97, Gran Sasso, Italy, 7-11 Sep 1997, Nucl. Phys. Suppl., A. Bottino, A.
di Credico and P. Monacelli (eds.). See also http://cfpa.berkeley.ed
Monte Carlo Simulation of Massive Absorbers for Cryogenic Calorimeters
There is a growing interest in cryogenic calorimeters with macroscopic absorbers for applications such as dark matter direct detection and rare event search experiments. The physics of energy transport in calorimeters with absorber masses exceeding several grams is made complex by the anisotropic nature of the absorber crystals as well as the changing mean free paths as phonons decay to progressively lower energies. We present a Monte Carlo model capable of simulating anisotropic phonon transport in cryogenic crystals. We have initiated the validation process and discuss the level of agreement between our simulation and experimental results reported in the literature, focusing on heat pulse propagation in germanium. The simulation framework is implemented using Geant4, a toolkit originally developed for high-energy physics Monte Carlo simulations. Geant4 has also been used for nuclear and accelerator physics, and applications in medical and space sciences. We believe that our current work may open up new avenues for applications in material science and condensed matter physics.United States. Dept. of Energy (SLAC National Accelerator Laboratory. Contract DE-AC02-76SF00515
Mixed Bino-Wino-Higgsino Dark Matter in Gauge Messenger Models
Almost degenerate bino and wino masses at the weak scale is one of unique
features of gauge messenger models. The lightest neutralino is a mixture of
bino, wino and higgsino and can produce the correct amount of the dark matter
density if it is the lightest supersymmetric particle. Furthermore, as a result
of squeezed spectrum of superpartners which is typical for gauge messenger
models, various co-annihilation and resonance regions overlap and very often
the correct amount of the neutralino relic density is generated as an interplay
of several processes. This feature makes the explanation of the observed amount
of the dark matter density much less sensitive to fundamental parameters. We
calculate the neutralino relic density assuming thermal history and present
both spin independent and spin dependent cross sections for the direct
detection. We also discuss phenomenological constraints from b to s gamma and
muon g-2 and compare results of gauge messenger models to well known results of
the mSUGRA scenario.Comment: 27 pages, 9 figures, references added, version to appear at JCA
Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors
We present results on quasidi usion studies in large, 3 inch diameter, 1 inch thick [100]
high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator,
and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare
data obtained in two di erent detector types, with di erent phonon sensor area coverage,
with results from a Monte Carlo. The Monte Carlo includes phonon quasidi usion and the
generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.United States. Dept. of Energy (Grant DE-FG02-04ER41295)United States. Dept. of Energy (Grant DE-FG02-07ER41480)National Science Foundation (U.S.) (Grant PHY-0542066)National Science Foundation (U.S.) (Grant PHY-0503729)National Science Foundation (U.S.) (Grant PHY-0503629)National Science Foundation (U.S.) (Grant PHY-0504224)National Science Foundation (U.S.) (Grant PHY-0705078)National Science Foundation (U.S.) (Grant PHY-0801712
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