61 research outputs found
Thermal detector model for cryogenic composite detectors for the dark matter experiments CRESST and EURECA
The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers)
and the EURECA (European Underground Rare Event Calorimeter Array) experiments
are direct dark matter search experiments where cryogenic detectors are used to
detect spin-independent, coherent WIMP (Weakly Interacting Massive
Particle)-nucleon scattering events by means of the recoil energy. The
cryogenic detectors use a massive single crystal as absorber which is equipped
with a TES (transition edge sensor) for signal read-out. They are operated at
mK-temperatures. In order to enable a mass production of these detectors, as
needed for the EURECA experiment, a so-called composite detector design (CDD)
that allows decoupling of the TES fabrication from the optimization procedure
of the absorber single-crystal was developed and studied. To further
investigate, understand and optimize the performance of composite detectors a
detailed thermal detector model which takes into account the CDD has been
developed.Comment: To appear in Journal of Physics: Conference Series; Proceedings of
Neutrino 2008, Christchurch, New Zealan
Solar and Atmospheric Neutrinos: Background Sources for the Direct Dark Matter Searches
In experiments for direct dark matter searches, neutrinos coherently
scattering off nuclei can produce similar events as Weakly Interacting Massive
Particles (WIMPs). The calculated count rate for solar neutrinos in such
experiments is a few events per ton-year. This count rate strongly depends on
the nuclear recoil energy threshold achieved in the experiments for the WIMP
search. We show that solar neutrinos can be a serious background source for
direct dark matter search experiments using Ge, Ar, Xe and CaWO_4 as target
materials. To reach sensitivities better than approximatly 10^-10 pb for the
elastic WIMP nucleon spin-independent cross section in the zero-background
limit, energy thresholds for nuclear recoils should be approximatly >2.05 keV
for CaWO_4, >4.91 keV for Ge, >2.89 keV for Xe, and >8.62 keV for Ar as target
material. Next-generation experiments should not only strive for a reduction of
the present energy thresholds but mainly focus on an increase of the target
mass. Atmospheric neutrinos limit the achievable sensitivity for the
background-free direct dark matter search to approximatly >10^-12 pb.Comment: accepted by Astroparticle Physic
Low-Temperature Light Detectors: Neganov-Luke Amplification and Calibration
The simultaneous measurement of phonons and scintillation light induced by
incident particles in a scintillating crystal such as CaWO4 is a powerful
technique for the active rejection of background induced by gamma's and beta's
and even neutrons in direct Dark Matter searches. However, less than ~1% of the
energy deposited in a CaWO4 crystal is detected as light. Thus, very sensitive
light detectors are needed for an efficient event-by-event background
discrimination. Due to the Neganov-Luke effect, the threshold of
low-temperature light detectors based on semiconducting substrates can be
improved significantly by drifting the photon-induced electron-hole pairs in an
applied electric field. We present measurements with low-temperature light
detectors based on this amplification mechanism. The Neganov-Luke effect makes
it possible to improve the signal-to-noise ratio of our light detectors by a
factor of ~9 corresponding to an energy threshold of ~21 eV. We also describe a
method for an absolute energy calibration using a light-emitting diode.Comment: additional figure, other figures improve
The CRESST II Dark Matter Search
Direct Dark Matter detection with cryodetectors is briefly discussed, with
particular mention of the possibility of the identification of the recoil
nucleus. Preliminary results from the CREEST II Dark Matter search, with 730
kg-days of data, are presented. Major backgrounds and methods of identifying
and dealing with them are indicated.Comment: Talk at DSU workshop, ITP Beijing, Oct. 2011. 9 figures, 2 table
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
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
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