54 research outputs found
A Search for WIMPs with the First Five-Tower Data from CDMS
We report first results from the Cryogenic Dark Matter Search (CDMS II)
experiment running with its full complement of 30 cryogenic particle detectors
at the Soudan Underground Laboratory. This report is based on the analysis of
data acquired between October 2006 and July 2007 from 15 Ge detectors (3.75
kg), giving an effective exposure of 121.3 kg-d (averaged over recoil energies
10--100 keV, weighted for a weakly interacting massive particle (WIMP) mass of
60 \gev). A blind analysis, incorporating improved techniques for event
reconstruction and data quality monitoring, resulted in zero observed events.
This analysis sets an upper limit on the WIMP-nucleon spin-independent cross
section of 6.6 cm (4.6 cm when combined
with previous CDMS Soudan data) at the 90% confidence level for a WIMP mass of
60 \gev. By providing the best sensitivity for dark matter WIMPs with masses
above 42 GeV/c, this work significantly restricts the parameter space for
some of the favored supersymmetric models.Comment: 5 pages, 4 figures, submitted to PRL 28 March 200
Low-threshold analysis of CDMS shallow-site data
Data taken during the final shallow-site run of the first tower of the
Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with
improved sensitivity to small energy depositions. Four ~224 g germanium and two
~105 g silicon detectors were operated at the Stanford Underground Facility
(SUF) between December 2001 and June 2002, yielding 118 live days of raw
exposure. Three of the germanium and both silicon detectors were analyzed with
a new low-threshold technique, making it possible to lower the germanium and
silicon analysis thresholds down to the actual trigger thresholds of ~1 keV and
~2 keV, respectively. Limits on the spin-independent cross section for weakly
interacting massive particles (WIMPs) to elastically scatter from nuclei based
on these data exclude interesting parameter space for WIMPs with masses below 9
GeV/c^2. Under standard halo assumptions, these data partially exclude
parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT
experiments' data as WIMP signals, and exclude new parameter space for WIMP
masses between 3 GeV/c^2 and 4 GeV/c^2.Comment: 18 pages, 12 figures, 5 table
New Results from the Cryogenic Dark Matter Search Experiment
Using improved Ge and Si detectors, better neutron shielding, and increased
counting time, the Cryogenic Dark Matter Search (CDMS) experiment has obtained
stricter limits on the cross section of weakly interacting massive particles
(WIMPs) elastically scattering from nuclei. Increased discrimination against
electromagnetic backgrounds and reduction of neutron flux confirm
WIMP-candidate events previously detected by CDMS were consistent with neutrons
and give limits on spin-independent WIMP interactions which are >2X lower than
previous CDMS results for high WIMP mass, and which exclude new parameter space
for WIMPs with mass between 8-20 GeV/c^2.Comment: 4 pages, 4 figure
Exclusion Limits on the WIMP-Nucleon Cross-Section from the First Run of the Cryogenic Dark Matter Search in the Soudan Underground Lab
The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si
detectors to seek Weakly Interacting Massive Particles (WIMPs) via their
elastic scattering interactions with nuclei. Simultaneous measurements of both
ionization and phonon energy provide discrimination against interactions of
background particles. For recoil energies above 10 keV, events due to
background photons are rejected with >99.99% efficiency. Electromagnetic events
very near the detector surface can mimic nuclear recoils because of reduced
charge collection, but these surface events are rejected with >96% efficiency
by using additional information from the phonon pulse shape. Efficient use of
active and passive shielding, combined with the the 2090 m.w.e. overburden at
the experimental site in the Soudan mine, makes the background from neutrons
negligible for this first exposure. All cuts are determined in a blind manner
from in situ calibrations with external radioactive sources without any prior
knowledge of the event distribution in the signal region. Resulting
efficiencies are known to ~10%. A single event with a recoil of 64 keV passes
all of the cuts and is consistent with the expected misidentification rate of
surface-electron recoils. Under the assumptions for a standard dark matter
halo, these data exclude previously unexplored parameter space for both
spin-independent and spin-dependent WIMP-nucleon elastic scattering. The
resulting limit on the spin-independent WIMP-nucleon elastic-scattering
cross-section has a minimum of 4x10^-43 cm^2 at a WIMP mass of 60 GeV/c^2. The
minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering
cross-section is 2x10^-37 cm^2 at a WIMP mass of 50 GeV/c^2.Comment: 37 pages, 42 figure
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
New results from the Cryogenic Dark Matter Search experiment
Using improved Ge and Si detectors, better neutron shielding, and increased counting time, the Cryogenic Dark Matter Search (CDMS) experiment has obtained stricter limits on the cross section of weakly interacting massive particles (WIMPs) elastically scattering from nuclei. Increased discrimination against electromagnetic backgrounds and reduction of the neutron flux confirm WIMP-candidate events previously detected by CDMS were consistent with neutrons and give limits on spin-independent WIMP interactions which are \u3e2× lower than previous CDMS results for high WIMP mass, and which exclude new parameter space for WIMPs with mass between 8 and 20 GeV/c2
Limits on spin-dependent WIMP-nucleon interactions from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) is an experiment to detect weakly
interacting massive particles (WIMPs) based on their interactions with Ge and
Si nuclei. We report the results of an analysis of data from the first two runs
of CDMS at the Soudan Underground Laboratory in terms of spin-dependent
WIMP-nucleon interactions on 73Ge and 29Si. These data exclude new regions of
spin-dependent WIMP-nucleon interaction parameter space, including regions
relevant to spin-dependent interpretations of the annual modulation signal
reported by the DAMA/NaI experiment.Comment: 5 pages, 4 figures; replacement to match published versio
An Ultra-Low Background PMT for Liquid Xenon Detectors
Results are presented from radioactivity screening of two models of
photomultiplier tubes designed for use in current and future liquid xenon
experiments. The Hamamatsu 5.6 cm diameter R8778 PMT, used in the LUX dark
matter experiment, has yielded a positive detection of four common radioactive
isotopes: 238U, 232Th, 40K, and 60Co. Screening of LUX materials has rendered
backgrounds from other detector materials subdominant to the R8778
contribution. A prototype Hamamatsu 7.6 cm diameter R11410 MOD PMT has also
been screened, with benchmark isotope counts measured at <0.4 238U / <0.3 232Th
/ <8.3 40K / 2.0+-0.2 60Co mBq/PMT. This represents a large reduction, equal to
a change of \times 1/24 238U / \times 1/9 232Th / \times 1/8 40K per PMT,
between R8778 and R11410 MOD, concurrent with a doubling of the photocathode
surface area (4.5 cm to 6.4 cm diameter). 60Co measurements are comparable
between the PMTs, but can be significantly reduced in future R11410 MOD units
through further material selection. Assuming PMT activity equal to the measured
90% upper limits, Monte Carlo estimates indicate that replacement of R8778 PMTs
with R11410 MOD PMTs will change LUX PMT electron recoil background
contributions by a factor of \times1/25 after further material selection for
60Co reduction, and nuclear recoil backgrounds by a factor of \times 1/36. The
strong reduction in backgrounds below the measured R8778 levels makes the
R11410 MOD a very competitive technology for use in large-scale liquid xenon
detectors.Comment: v2 updated to include content after reviewer comments (Sep 2012
Creating positive environmental impact through citizen science
Interest in citizen science is growing, including from governments and research funders. This interest is often driven by a desire for positive environmental impact, and the expectation that citizen science can deliver it by engaging the public and simultaneously collecting environmental data. Yet, in practice, there is often a gap between expected and realised impact. To close this gap, we need to better understand pathways to impact and what it takes to realise them. We articulate six key pathways through which citizen science can create positive environmental change: (1) environmental management; (2) evidence for policy; (3) behaviour change; (4) social network championing; (5) political advocacy; and (6) community action. We explore the project attributes likely to create impact through each of these pathways and show that there is an interplay between these project attributes and the needs and motivations of target participant groups. Exploring this interplay, we create a framework that articulates four citizen science approaches that create environmental impact in different ways: place-based community action; interest group investigation; captive learning research; and mass participation census
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