103 research outputs found
Experimental evidence for a surface distribution of two-level systems in superconducting lithographed microwave resonators
We present measurements of the temperature-dependent frequency shift of five
niobium superconducting coplanar waveguide microresonators with center strip
widths ranging from 3 m to 50 m, taken at temperatures in the range
100-800 mK, far below the 9.2 K transition temperature of niobium. These data
agree well with the two-level system (TLS) theory. Fits to this theory provide
information on the number of TLS that interact with each resonator geometry.
The geometrical scaling indicates a surface distribution of TLS, and the data
are consistent with a TLS surface layer thickness of order a few nm, as might
be expected for a native oxide layer.Comment: 3 figures, submitted to AP
Particle astrophysics
The following scientific areas are reviewed: (1) cosmology and particle physics (particle physics and the early universe, dark matter, and other relics); (2) stellar physics and particles (solar neutrinos, supernovae, and unconventional particle physics); (3) high energy gamma ray and neutrino astronomy; (4) cosmic rays (space and ground observations). Highest scientific priorities for the next decade include implementation of the current program, new initiatives, and longer-term programs. Essential technological developments, such as cryogenic detectors of particles, new solar neutrino techniques, and new extensive air shower detectors, are discussed. Also a certain number of institutional issues (the funding of particle astrophysics, recommended funding mechanisms, recommended facilities, international collaborations, and education and technology) which will become critical in the coming decade are presented
Collection of Athermal Phonons into Doped Germanium Thermistors Using Quasiparticle Trapping
We have developed a low‐temperature particle detector that uses a novel quasiparticle trapping mechanism to funnel athermal phonon energy from an 80 mg Ge absorber into a 1.6 mg doped Ge thermistor via a superconducting Al film. We report on pulse height spectra obtained at 320 mK by scanning a 241Am alpha source along the device, and show that up to 20% of the energy deposited in the Ge absorber by a 5.5 MeV alpha particle interaction can be collected into a thermistor via quasiparticle trapping. We show that this device is sensitive to the position of an alpha particle interaction in the Ge absorber for interaction distances of up to 5 mm from a quasiparticle trap
A semi-empirical model for two-level system noise in superconducting microresonators
We present measurements of the low--temperature excess frequency noise of
four niobium superconducting coplanar waveguide microresonators, with center
strip widths ranging from 3 m to 20 m. For a fixed internal
power, we find that the frequency noise decreases rapidly with increasing
center strip width, scaling as . We show that this geometrical
scaling is readily explained by a simple semi-empirical model which assumes a
surface distribution of independent two-level system fluctuators. These results
allow the resonator geometry to be optimized for minimum noise.Comment: 3 fig
Model-Independent Comparison of Direct vs. Indirect Detection of Supersymmetric Dark Matter
We compare the rate for elastic scattering of neutralinos from various nuclei
with the flux of upward muons induced by energetic neutrinos from neutralino
annihilation in the Sun and Earth. We consider both scalar and axial-vector
interactions of neutralinos with nuclei. We find that the event rate in a kg of
germanium is roughly equivalent to that in a - to -m muon
detector for a neutralino with primarily scalar coupling to nuclei. For an
axially coupled neutralino, the event rate in a 50-gram hydrogen detector is
roughly the same as that in a 10- to 500-m muon detector. Expected
experimental backgrounds favor forthcoming elastic-scattering detectors for
scalar couplings while the neutrino detectors have the advantage for
axial-vector couplings.Comment: 10 pages, self-unpacking uuencoded PostScript fil
Measurement of ionization and phonon production by nuclear recoils in a 60 g crystal of germanium at 25 mK
We report on the first measurement of the absolute phonon energy and the amount of ionization produced by the recoil of nuclei and electrons in a 60 g germanium cyrstal at a temperature of ≊25 mK. We find good agreement between our results and previous measurements of ionization yield from nuclear recoils in germanium. Our device achieves 10:1 discrimination between neutrons and photons in the few keV energy range, demonstrating the feasibility of this technique for large reductions of background in searches for direct interactions of weakly interacting massive particle dark matter
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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
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