58 research outputs found
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
Exploiting data locality in Swift/T workflows using Hercules
The ever-increasing power of supercomputer systems is both driving and enabling the emergence of new problem-solving methods that require the efficient execution of many concurrent and interacting tasks. Swift/T, as a description language and runtime, offers the dynamic creation and execution of workflows, varying in granularity, on high-component-count platforms. Swift/T takes advantage of the Asynchronous Dynamic Load Balancing (ADLB) library to dynamically distribute the tasks among the nodes. These tasks may share data using a parallel file system, an approach that could degrade performance as a result of interference with other applications and poor exploitation of data locality. The objective of this work is to expose and exploit data locality in Swift/T through Hercules, a distributed in-memory store based on Memcached, and to explore tradeoffs between data locality and load balance in distributed workflow executions. In this paper we present our approach to enable locality-based optimizations in Swift/T by guiding ADLB to schedule computation jobs in the nodes containing the required data. We also analyze the interaction between locality and load balance: our initial measurements based on various raw file access patterns show promising results. Moreover, we present future work based on the promising results achieved so far.This material is based upon work supported by the U.S. Department of Energy, Office of Science, under contract DE-AC02-06CH11357. Computing resources were provided by the Argonne Leadership Computing Facility. The work presented in this paper was supported by the COST Action IC1305, âNetwork for Sustainable Ultrascale
Computing (NESUS).â The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 328582
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
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
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