867 research outputs found
The -cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering
We discuss a small-scale experiment, called -cleus, for the first
detection of coherent neutrino-nucleus scattering by probing nuclear-recoil
energies down to the 10 eV-regime. The detector consists of low-threshold
CaWO and AlO calorimeter arrays with a total mass of about 10 g and
several cryogenic veto detectors operated at millikelvin temperatures.
Realizing a fiducial volume and a multi-element target, the detector enables
active discrimination of , neutron and surface backgrounds. A first
prototype AlO device, operated above ground in a setup without
shielding, has achieved an energy threshold of eV and further
improvements are in reach. A sensitivity study for the detection of coherent
neutrino scattering at nuclear power plants shows a unique discovery potential
(5) within a measuring time of weeks. Furthermore, a site
at a thermal research reactor and the use of a radioactive neutrino source are
investigated. With this technology, real-time monitoring of nuclear power
plants is feasible.Comment: 14 pages, 19 figure
The CRESST Experiment: Recent Results and Prospects
The CRESST experiment seeks hypothetical WIMP particles that could account
for the bulk of dark matter in the Universe. The detectors are cryogenic
calorimeters in which WIMPs would scatter elastically on nuclei, releasing
phonons. The first phase of the experiment has successfully deployed several
262 g sapphire devices in the Gran Sasso underground laboratories. A main
source of background has been identified as microscopic mechanical fracturing
of the crystals, and has been eliminated, improving the background rate by up
to three orders of magnitude at low energies, leaving a rate close to one count
per day per kg and per keV above 10 keV recoil energy. This background now
appears to be dominated by radioactivity, and future CRESST scintillating
calorimeters which simultaneously measure light and phonons will allow
rejection of a great part of it.Comment: To appear in the proceedings of the CAPP2000 Conference, Verbier,
Switzerland, July, 2000 (eds J. Garcia-Bellido, R. Durrer, and M.
Shaposhnikov
Observation of out-of-phase bilayer plasmons in YBa_2Cu_3O_7-delta
The temperature dependence of the c-axis optical conductivity \sigma(\omega)
of optimally and overdoped YBa_2Cu_3O_x (x=6.93 and 7) is reported in the far-
(FIR) and mid-infrared (MIR) range. Below T_c we observe a transfer of spectral
weight from the FIR not only to the condensate at \omega = 0, but also to a new
peak in the MIR. This peak is naturally explained as a transverse out-of-phase
bilayer plasmon by a model for \sigma(\omega) which takes the layered crystal
structure into account. With decreasing doping the plasmon shifts to lower
frequencies and can be identified with the surprising and so far not understood
FIR feature reported in underdoped bilayer cuprates.Comment: 7 pages, 3 eps figures, Revtex, epsfi
The anomaly of the oxygen bond-bending mode at 320 cm and the additional absorption peak in the c-axis infrared conductivity of underdoped YBaCuO single crystals revisited by ellipsometricmeasurements
We have performed ellipsometric measurements of the far-infrared c-axis
dielectric response of underdoped YBaCuO single
crystals. Here we report a detailed analysis of the temperature-dependent
renormalization of the oxygen bending phonon mode at 320 cm and the
formation of the additional absorption peak around 400-500 cm. For a
strongly underdoped YBaCuO crystal with T=52 K we
find that, in agreement with previous reports based on conventional reflection
measurements, the gradual onset of both features occurs well above T at
T*150 K. Contrary to some of these reports, however, our data establish
that the phonon anomaly and the formation of the additional peak exhibit very
pronounced and steep changes right at T. For a less underdoped
YBaCuO crystal with T=80 K, the onset temperature of
the phonon anomaly almost coincides with T. Also in contrast to some
previous reports, we find for both crystals that a sizeable fraction of the
spectral weight of the additional absorption peak cannot be accounted for by
the spectral-weight loss of the phonon modes but instead arises from a
redistribution of the electronic continuum. Our ellipsometric data are
consistent with a model where the bilayer cuprate compounds are treated as a
superlattice of intra- and inter-bilayer Josephson-junctions
Phonon anomalies and electron-phonon interaction in RuSr_2GdCu_2O_8 ferromagnetic superconductor: Evidence from infrared conductivity
Critical behavior of the infrared reflectivity of RuSr_2GdCu_2O_8 ceramics is
observed near the superconducting T_{SC} = 45 K and magnetic T_M = 133 K
transition temperatures. The optical conductivity reveals the typical features
of the c-axis optical conductivity of strongly underdoped multilayer
superconducting cuprates. The transformation of the Cu-O bending mode at 288
cm^{-1} to a broad absorption peak at the temperatures between T^* = 90 K and
T_{SC} is clearly observed, and is accompanied by the suppression of spectral
weight at low frequencies. The correlated shifts to lower frequencies of the
Ru-related phonon mode at 190 cm^{-1} and the mid-IR band at 4800 cm^{-1} on
decreasing temperature below T_M are observed. It provides experimental
evidence in favor of strong electron-phonon coupling of the charge carriers in
the Ru-O layers which critically depends on the Ru core spin alignment. The
underdoped character of the superconductor is explained by strong hole
depletion of the CuO_2 planes caused by the charge carrier self-trapping at the
Ru moments.Comment: 11 pages incl. 5 figures, submitted to PR
Self-Dual Bending Theory for Vesicles
We present a self-dual bending theory that may enable a better understanding
of highly nonlinear global behavior observed in biological vesicles. Adopting
this topological approach for spherical vesicles of revolution allows us to
describe them as frustrated sine-Gordon kinks. Finally, to illustrate an
application of our results, we consider a spherical vesicle globally distorted
by two polar latex beads.Comment: 10 pages, 3 figures, LaTeX2e+IOPar
Particle Discrimination in TeO Bolometers using Light Detectors read out by Transition Edge Sensors
An active discrimination of the dominant -background is the
prerequisite for future neutrinoless double-beta decay experiments based on
TeO bolometers. We investigate such -particle rejection in
cryogenic TeO bolometers by the detection of Cherenkov light. For a setup
consisting of a massive TeO crystal (285 g) and a separate cryogenic
light detector, both using transition edge sensors as temperature sensors
operated at around 10 mK, we obtain an event-by-event identification of
e/- and -events. We find in the energy interval ranging from
2400 keV to 2800 keV and covering the Q-value of the neutrinoless double-beta
decay of Te a separation of the means of the two populations of 3.7
times their width.Comment: 8 pages, 7 figure
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