470 research outputs found
The CRESST Dark Matter Search
We present first competitive results on WIMP dark matter using the
phonon-light-detection technique. A particularly strong limit for WIMPs with
coherent scattering results from selecting a region of the phonon-light plane
corresponding to tungsten recoils. The observed count rate in the neutron band
is compatible with the rate expected from neutron background. CRESST is
presently being upgraded with a 66 channel SQUID readout system, a neutron
shield and a muon veto system. This results in a significant improvement in
sensitivity.Comment: 6 pages, 3 figures, to be published in the proceedings of the 5th
International Workshop on the Identification and Detection of Dark Matter IDM
2004, Edinburgh, Sept. 2004, World Scientifi
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
Optical Scattering Lengths in Large Liquid-Scintillator Neutrino Detectors
For liquid-scintillator neutrino detectors of kiloton scale, the transparency
of the organic solvent is of central importance. The present paper reports on
laboratory measurements of the optical scattering lengths of the organic
solvents PXE, LAB, and Dodecane which are under discussion for next-generation
experiments like SNO+, Hanohano, or LENA. Results comprise the wavelength range
from 415 to 440nm. The contributions from Rayleigh and Mie scattering as well
as from absorption/re-emission processes are discussed. Based on the present
results, LAB seems to be the preferred solvent for a large-volume detector.Comment: 9 pages, 3 figures, accepted for publication by Rev. Scient. Instr
Results from 730 kg days of the CRESST-II Dark Matter Search
The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via
elastic scattering off nuclei in CaWO crystals, completed 730 kg days of
data taking in 2011. We present the data collected with eight detector modules,
each with a two-channel readout; one for a phonon signal and the other for
coincidently produced scintillation light. The former provides a precise
measure of the energy deposited by an interaction, and the ratio of
scintillation light to deposited energy can be used to discriminate different
types of interacting particles and thus to distinguish possible signal events
from the dominant backgrounds. Sixty-seven events are found in the acceptance
region where a WIMP signal in the form of low energy nuclear recoils would be
expected. We estimate background contributions to this observation from four
sources: 1) "leakage" from the e/\gamma-band 2) "leakage" from the
\alpha-particle band 3) neutrons and 4) Pb-206 recoils from Po-210 decay. Using
a maximum likelihood analysis, we find, at a high statistical significance,
that these sources alone are not sufficient to explain the data. The addition
of a signal due to scattering of relatively light WIMPs could account for this
discrepancy, and we determine the associated WIMP parameters.Comment: 17 pages, 13 figure
Recoilless resonant neutrino capture and basics of neutrino oscillations
It is shown that the experiment on recoilless resonant emission and
absorption of , proposed recently by Raghavan, could have an
important impact on our understanding of the physics of neutrino oscillations.Comment: Additional information in the last chapte
Detection of the Natural Alpha Decay of Tungsten
The natural alpha decay of 180W has been unambiguously detected for the first
time. The alpha peak is found in a (gamma,beta and neutron)-free background
spectrum. This has been achieved by the simultaneous measurement of phonon and
light signals with the CRESST cryogenic detectors. A half-life of T1/2 = (1.8
+- 0.2) x 10^18 y and an energy release of Q = (2516.4 +- 1.1 (stat.) +- 1.2
(sys.)) keV have been measured. New limits are also set on the half-lives of
the other naturally occurring tungsten isotopes.Comment: Submitted to Physical Review C Revised versio
Status of the CRESST Dark Matter Search
The CRESST experiment aims for a detection of dark matter in the form of
WIMPs. These particles are expected to scatter elastically off the nuclei of a
target material, thereby depositing energy on the recoiling nucleus. CRESST
uses scintillating CaWO4 crystals as such a target. The energy deposited by an
interacting particle is primarily converted to phonons which are detected by
transition edge sensors. In addition, a small fraction of the interaction
energy is emitted from the crystals in the form of scintillation light which is
measured in coincidence with the phonon signal by a separate cryogenic light
detector for each target crystal. The ratio of light to phonon energy permits
the discrimination between the nuclear recoils expected from WIMPs and events
from radioactive backgrounds which primarily lead to electron recoils. CRESST
has shown the success of this method in a commissioning run in 2007 and, since
then, further investigated possibilities for an even better suppression of
backgrounds. Here, we report on a new class of background events observed in
the course of this work. The consequences of this observation are discussed and
we present the current status of the experiment.Comment: Proceedings of the 13th International Workshop on Low Temperature
Detectors, 4 pages, 3 figure
Composite CaWO4 Detectors for the CRESST-II Experiment
CRESST-II, standing for Cryogenic Rare Events Search with Superconducting
Thermometers phase II, is an experiment searching for Dark Matter. In the LNGS
facility in Gran Sasso, Italy, a cryogenic detector setup is operated in order
to detect WIMPs by elastic scattering off nuclei, generating phononic lattice
excitations and scintillation light. The thermometers used in the experiment
consist of a tungsten thin-film structure evaporated onto the CaWO4 absorber
crystal. The process of evaporation causes a decrease in the scintillation
light output. This, together with the need of a big-scale detector production
for the upcoming EURECA experiment lead to investigations for producing
thermometers on smaller crystals which are glued onto the absorber crystal. In
our Run 31 we tested composite detectors for the first time in the Gran Sasso
setup. They seem to produce higher light yields as hoped and could provide an
additional time based discrimination mechanism for low light yield clamp
events.Comment: Proceedings of the Thirteenth International Workshop on Low
Temperature Detectors 4 pages, 9 figure
Neutrino oscillations and uncertainty relations
We show that coherent flavor neutrino states are produced (and detected) due
to the momentum-coordinate Heisenberg uncertainty relation. The Mandelstam-Tamm
time-energy uncertainty relation requires non-stationary neutrino states for
oscillations to happen and determines the time interval (propagation length)
which is necessary for that. We compare different approaches to neutrino
oscillations which are based on different physical assumptions but lead to the
same expression for the neutrino transition probability in standard neutrino
oscillation experiments. We show that a Moessbauer neutrino experiment could
allow to distinguish different approaches and we present arguments in favor of
the 163Ho-163Dy system for such an experiment.Comment: Some small changes in section 2, results unchanged. Added referenc
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