207 research outputs found
CsI(Tl) for WIMP dark matter searches
We report a study of CsI(Tl) scintillator to assess its applicability in
experiments to search for dark matter particles. Measurements of the mean
scintillation pulse shapes due to nuclear and electron recoils have been
performed. We find that, as with NaI(Tl), pulse shape analysis can be used to
discriminate between electron and nuclear recoils down to 4 keV. However, the
discrimination factor is typically (10-15)% better than in NaI(Tl) above 4 keV.
The quenching factor for caesium and iodine recoils was measured and found to
increase from 11% to ~17% with decreasing recoil energy from 60 to 12 keV.
Based on these results, the potential sensitivity of CsI(Tl) to dark matter
particles in the form of neutralinos was calculated. We find an improvement
over NaI(Tl) for the spin independent WIMP-nucleon interactions up to a factor
of 5 assuming comparable electron background levels in the two scintillators.Comment: 16 pages, 8 figures, to be published in Nucl. Instrum. and Meth. in
Phys. Res.
Simulations of neutron background in a time projection chamber relevant to dark matter searches
Presented here are results of simulations of neutron background performed for
a time projection chamber acting as a particle dark matter detector in an
underground laboratory. The investigated background includes neutrons from rock
and detector components, generated via spontaneous fission and (alpha, n)
reactions, as well as those due to cosmic-ray muons. Neutrons were propagated
to the sensitive volume of the detector and the nuclear recoil spectra were
calculated. Methods of neutron background suppression were also examined and
limitations to the sensitivity of a gaseous dark matter detector are discussed.
Results indicate that neutrons should not limit sensitivity to WIMP-nucleon
interactions down to a level of (1 - 3) x 10^{-8} pb in a 10 kg detector.Comment: 27 pages (total, including 3 tables and 11 figures). Accepted for
publication in Nuclear Instruments and Methods in Physics Research - Section
Measurements of Scintillation Efficiency and Pulse-Shape for Low Energy Recoils in Liquid Xenon
Results of observations of low energy nuclear and electron recoil events in
liquid xenon scintillator detectors are given. The relative scintillation
efficiency for nuclear recoils is 0.22 +/- 0.01 in the recoil energy range 40
keV - 70 keV. Under the assumption of a single dominant decay component to the
scintillation pulse-shape the log-normal mean parameter T0 of the maximum
likelihood estimator of the decay time constant for 6 keV < Eee < 30 keV
nuclear recoil events is equal to 21.0 ns +/- 0.5 ns. It is observed that for
electron recoils T0 rises slowly with energy, having a value ~ 30 ns at Eee ~
15 keV. Electron and nuclear recoil pulse-shapes are found to be well fitted by
single exponential functions although some evidence is found for a double
exponential form for the nuclear recoil pulse-shape.Comment: 11 pages, including 5 encapsulated postscript figure
Neutron background in large-scale xenon detectors for dark matter searches
Simulations of the neutron background for future large-scale particle dark
matter detectors are presented. Neutrons were generated in rock and detector
elements via spontaneous fission and (alpha,n) reactions, and by cosmic-ray
muons. The simulation techniques and results are discussed in the context of
the expected sensitivity of a generic liquid xenon dark matter detector.
Methods of neutron background suppression are investigated. A sensitivity of
pb to WIMP-nucleon interactions can be achieved by a
tonne-scale detector.Comment: 35 pages, 13 figures, 2 tables, accepted for publication in
Astroparticle Physic
First Results from the DRIFT-IIa Dark Matter Detector
Data from the DRIFT-IIa directional dark matter experiment are presented,
collected during a near continuous 6 month running period. A detailed
calibration analysis comparing data from gamma-ray, x-ray and neutron sources
to a GEANT4 Monte Carlo simulations reveals an efficiency for detection of
neutron induced recoils of 94+/-2(stat.)+/-5(sys.)%. Software-based cuts,
designed to remove non-nuclear recoil events, are shown to reject 60Co
gamma-rays with a rejection factor of better than 8x10-6 for all energies above
threshold. An unexpected event population has been discovered and is shown here
to be due to the alpha-decay of 222Rn daughter nuclei that have attached to the
central cathode. A limit on the flux of neutrons in the Boulby Underground
Laboratory is derived from analysis of unshielded and shielded data.Comment: 43 pages, 14 figures, submitted to Astroparticle Physic
Track Reconstruction and Performance of DRIFT Directional Dark Matter Detectors using Alpha Particles
First results are presented from an analysis of data from the DRIFT-IIa and
DRIFT-IIb directional dark matter detectors at Boulby Mine in which alpha
particle tracks were reconstructed and used to characterise detector
performance--an important step towards optimising directional technology. The
drift velocity in DRIFT-IIa was [59.3 +/- 0.2 (stat) +/- 7.5 (sys)] m/s based
on an analysis of naturally-occurring alpha-emitting background. The drift
velocity in DRIFT-IIb was [57 +/- 1 (stat) +/- 3 (sys)] m/s determined by the
analysis of alpha particle tracks from a Po-210 source. 3D range reconstruction
and energy spectra were used to identify alpha particles from the decay of
Rn-222, Po-218, Rn-220 and Po-216. This study found that (22 +/- 2)% of Po-218
progeny (from Rn-222 decay) are produced with no net charge in 40 Torr CS2. For
Po-216 progeny (from Rn-220 decay) the uncharged fraction is (100 +0 -35)%.Comment: 27 pages, 12 figures, 5 tables. Submitted to Nuclear Instruments and
Methods in Physics Research, Section A. Subj-class: Instrumentation and
Detector
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
Amniotic ectoderm expansion in mouse occurs via distinct modes and requires SMAD5-mediated signalling
Stem cells & developmental biolog
Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data
The first underground data run of the ZEPLIN-II experiment has set a limit on
the nuclear recoil rate in the two-phase xenon detector for direct dark matter
searches. In this paper the results from this run are converted into the limits
on spin-dependent WIMP-proton and WIMP-neutron cross-sections. The minimum of
the curve for WIMP-neutron cross-section corresponds to 0.07 pb at a WIMP mass
of around 65 GeV.Comment: 12 pages, 2 figures, to be published in Physics Letters
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