417 research outputs found
Exclusion limits on the WIMP-nucleon cross-section from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si
detectors to search for Weakly Interacting Massive Particles (WIMPs) via their
elastic-scattering interactions with nuclei while discriminating against
interactions of background particles. For recoil energies above 10 keV, events
due to background photons are rejected with >99.9% efficiency, and surface
events are rejected with >95% efficiency. The estimate of the background due to
neutrons is based primarily on the observation of multiple-scatter events that
should all be neutrons. Data selection is determined primarily by examining
calibration data and vetoed events. Resulting efficiencies should be accurate
to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed
fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent
with an earlier analysis with a more restrictive fiducial-volume cut.
Twenty-three WIMP candidate events are observed, but these events are
consistent with a background from neutrons in all ways tested. Resulting limits
on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude
unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}.
These limits border, but do not exclude, parameter space allowed by
supersymmetry models and accelerator constraints. Results are compatible with
some regions reported as allowed at 3-sigma by the annual-modulation
measurement of the DAMA collaboration. However, under the assumptions of
standard WIMP interactions and a standard halo, the results are incompatible
with the DAMA most likely value at >99.9% CL, and are incompatible with the
model-independent annual-modulation signal of DAMA at 99.99% CL in the
asymptotic limit.Comment: 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D;
v.2:clarified conclusions, added content and references based on referee's
and readers' comments; v.3: clarified introductory sections, added figure
based on referee's comment
Nuclear Shell Model Calculations of Neutralino-Nucleus Cross Sections for Silicon 29 and Germanium 73
We present the results of detailed nuclear shell model calculations of the
spin-dependent elastic cross section for neutralinos scattering from \si29 and
\ge73. The calculations were performed in large model spaces which adequately
describe the configuration mixing in these two nuclei. As tests of the computed
nuclear wave functions, we have calculated several nuclear observables and
compared them with the measured values and found good agreement. In the limit
of zero momentum transfer, we find scattering matrix elements in agreement with
previous estimates for \si29 but significantly different than previous work for
\ge73. A modest quenching, in accord with shell model studies of other heavy
nuclei, has been included to bring agreement between the measured and
calculated values of the magnetic moment for \ge73. Even with this quenching,
the calculated scattering rate is roughly a factor of 2 higher than the best
previous estimates; without quenching, the rate is a factor of 4 higher. This
implies a higher sensitivity for germanium dark matter detectors. We also
investigate the role of finite momentum transfer upon the scattering response
for both nuclei and find that this can significantly change the expected rates.
We close with a brief discussion of the effects of some of the non-nuclear
uncertainties upon the matrix elements.Comment: 31 pages, figures avaiable on request, UCRL-JC-11408
The Nylon Scintillator Containment Vessels for the Borexino Solar Neutrino Experiment
Borexino is a solar neutrino experiment designed to observe the 0.86 MeV Be-7
neutrinos emitted in the pp cycle of the sun. Neutrinos will be detected by
their elastic scattering on electrons in 100 tons of liquid scintillator. The
neutrino event rate in the scintillator is expected to be low (~0.35 events per
day per ton), and the signals will be at energies below 1.5 MeV, where
background from natural radioactivity is prominent. Scintillation light
produced by the recoil electrons is observed by an array of 2240
photomultiplier tubes. Because of the intrinsic radioactive contaminants in
these PMTs, the liquid scintillator is shielded from them by a thick barrier of
buffer fluid. A spherical vessel made of thin nylon film contains the
scintillator, separating it from the surrounding buffer. The buffer region
itself is divided into two concentric shells by a second nylon vessel in order
to prevent inward diffusion of radon atoms. The radioactive background
requirements for Borexino are challenging to meet, especially for the
scintillator and these nylon vessels. Besides meeting requirements for low
radioactivity, the nylon vessels must also satisfy requirements for mechanical,
optical, and chemical properties. The present paper describes the research and
development, construction, and installation of the nylon vessels for the
Borexino experiment
The CRESST Dark Matter Search
The current status of CRESST (Cryogenic Rare Event Search using
Superconducting Thermometers) and new results concerning the detector
development are presented. The basic technique of CRESST is to search for
particle Dark Matter (WIMPS, Weakly Interacting Massive particles) by the
measurement of non-thermal phonons as created by WIMP-induced nuclear recoils.
Combined with the newly developed method of simultaneous measurement of
scintillation light, strong background discrimination is possible, resulting in
a substantial increase in WIMP detection sensitivity. The short and long term
perspectives of CRESST are discussed.Comment: 12 pages, 6 figure
First Results from the XENON10 Dark Matter Experiment at the Gran Sasso National Laboratory
The XENON10 experiment at the Gran Sasso National Laboratory uses a 15 kg
xenon dual phase time projection chamber (XeTPC) to search for dark matter
weakly interacting massive particles (WIMPs). The detector measures
simultaneously the scintillation and the ionization produced by radiation in
pure liquid xenon, to discriminate signal from background down to 4.5 keV
nuclear recoil energy. A blind analysis of 58.6 live days of data, acquired
between October 6, 2006 and February 14, 2007, and using a fiducial mass of 5.4
kg, excludes previously unexplored parameter space, setting a new 90% C.L.
upper limit for the WIMP-nucleon spin-independent cross-section of 8.8 x
10^{-44} cm^2 for a WIMP mass of 100 GeV/c^2, and 4.5 x 10^{-44} cm^2 for a
WIMP mass of 30 GeV/c^2. This result further constrains predictions of
supersymmetric models.Comment: accepted for publication in Phys. Rev. Let
3D Position Sensitive XeTPC for Dark Matter Search
The technique to realize 3D position sensitivity in a two-phase xenon time
projection chamber (XeTPC) for dark matter search is described. Results from a
prototype detector (XENON3) are presented.Comment: Presented at the 7th UCLA Symposium on "Sources and Detection of Dark
Matter and Dark Energy in the Universe
Status of the LUX Dark Matter Search
The Large Underground Xenon (LUX) dark matter search experiment is currently
being deployed at the Homestake Laboratory in South Dakota. We will highlight
the main elements of design which make the experiment a very strong competitor
in the field of direct detection, as well as an easily scalable concept. We
will also present its potential reach for supersymmetric dark matter detection,
within various timeframes ranging from 1 year to 5 years or more.Comment: 4 pages, in proceedings of the SUSY09 conferenc
Constraints on inelastic dark matter from XENON10
It has been suggested that dark matter particles which scatter inelastically
from detector target nuclei could explain the apparent incompatibility of the
DAMA modulation signal (interpreted as evidence for particle dark matter) with
the null results from CDMS-II and XENON10. Among the predictions of
inelastically interacting dark matter are a suppression of low-energy events,
and a population of nuclear recoil events at higher nuclear recoil equivalent
energies. This is in stark contrast to the well-known expectation of a falling
exponential spectrum for the case of elastic interactions. We present a new
analysis of XENON10 dark matter search data extending to E keV
nuclear recoil equivalent energy. Our results exclude a significant region of
previously allowed parameter space in the model of inelastically interacting
dark matter. In particular, it is found that dark matter particle masses
GeV are disfavored.Comment: 8 pages, 4 figure
A search for light dark matter in XENON10 data
We report results of a search for light (<10 GeV) particle dark matter with
the XENON10 detector. The event trigger was sensitive to a single electron,
with the analysis threshold of 5 electrons corresponding to 1.4 keV nuclear
recoil energy. Considering spin-independent dark matter-nucleon scattering, we
exclude cross sections \sigma_n>3.5x10^{-42} cm^2, for a dark matter particle
mass m_{\chi}=8 GeV. We find that our data strongly constrain recent elastic
dark matter interpretations of excess low-energy events observed by CoGeNT and
CRESST-II, as well as the DAMA annual modulation signal.Comment: Manuscript identical to v2 (published version) but also contains
erratum. Note v3==v2 but without \linenumber
The interaction between a sexually transferred steroid hormone and a female protein regulates oogenesis in the malaria mosquito anopheles gambiae
Molecular interactions between male and female factors during mating profoundly affect the reproductive behavior and physiology of female insects. In natural populations of the malaria mosquito Anopheles gambiae, blood-fed females direct nutritional resources towards oogenesis only when inseminated. Here we show that the mating-dependent pathway of egg development in these mosquitoes is regulated by the interaction between the steroid hormone 20-hydroxy-ecdysone (20E) transferred by males during copulation and a female Mating-Induced Stimulator of Oogenesis (MISO) protein. RNAi silencing of MISO abolishes the increase in oogenesis caused by mating in blood-fed females, causes a delay in oocyte development, and impairs the function of male-transferred 20E. Co-immunoprecipitation experiments show that MISO and 20E interact in the female reproductive tract. Moreover MISO expression after mating is induced by 20E via the Ecdysone Receptor, demonstrating a close cooperation between the two factors. Male-transferred 20E therefore acts as a mating signal that females translate into an increased investment in egg development via a MISO-dependent pathway. The identification of this male–female reproductive interaction offers novel opportunities for the control of mosquito populations that transmit malaria
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