139 research outputs found
Results from a Search for Light-Mass Dark Matter with a P-type Point Contact Germanium Detector
We report on several features present in the energy spectrum from an ultra
low-noise germanium detector operated at 2,100 m.w.e. By implementing a new
technique able to reject surface events, a number of cosmogenic peaks can be
observed for the first time. We discuss several possible causes for an
irreducible excess of bulk-like events below 3 keVee, including a dark matter
candidate common to the DAMA/LIBRA annual modulation effect, the hint of a
signal in CDMS, and phenomenological predictions. Improved constraints are
placed on a cosmological origin for the DAMA/LIBRA effect.Comment: 4 pages, 4 figures. v2: submitted version. Minimal changes in
wording, one reference adde
Search for an Annual Modulation in a P-type Point Contact Germanium Dark Matter Detector
Fifteen months of cumulative CoGeNT data are examined for indications of an
annual modulation, a predicted signature of Weakly Interacting Massive Particle
(WIMP) interactions. Presently available data support the presence of a
modulated component of unknown origin, with parameters prima facie compatible
with a galactic halo composed of light-mass WIMPs. Unoptimized estimators yield
a statistical significance for a modulation of ~2.8 sigma, limited by the short
exposure.Comment: Published version, slightly expanded discussion of ROI uncertainties,
one reference adde
The MAJORANA DEMONSTRATOR: A Search for Neutrinoless Double-beta Decay of Germanium-76
The observation of neutrinoless double-beta decay would determine whether the
neutrino is a Majorana particle and provide information on the absolute scale
of neutrino mass. The MAJORANA Collaboration is constructing the DEMONSTRATOR,
an array of germanium detectors, to search for neutrinoless double-beta decay
of 76-Ge. The DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be
enriched to 86% in 76-Ge. The DEMONSTRATOR will be deployed deep underground in
an ultra-low-background shielded environment. Operation of the DEMONSTRATOR
aims to determine whether a future tonne-scale germanium experiment can achieve
a background goal of one count per tonne-year in a 4-keV region of interest
around the 76-Ge neutrinoless double-beta decay Q-value of 2039 keV.Comment: Submitted to AIP Conference Proceedings, 19th Particles & Nuclei
International Conference (PANIC 2011), Massachusetts Institute of Technology,
Cambridge, MA, USA, July 24-29, 2011; 3 pages, 1 figur
The Majorana Project
Building a \BBz experiment with the ability to probe neutrino mass in the
inverted hierarchy region requires the combination of a large detector mass
sensitive to \BBz, on the order of 1-tonne, and unprecedented background
levels, on the order of or less than 1 count per year in the \BBz signal
region. The MAJORANA Collaboration proposes a design based on using high-purity
enriched Ge-76 crystals deployed in ultra-low background electroformed Cu
cryostats and using modern analysis techniques that should be capable of
reaching the required sensitivity while also being scalable to a 1-tonne size.
To demonstrate feasibility, the collaboration plans to construct a prototype
system, the MAJORANA DEMONSTRATOR, consisting of 30 kg of 86% enriched \Ge-76
detectors and 30 kg of natural or isotope-76-depleted Ge detectors. We plan to
deploy and evaluate two different Ge detector technologies, one based on a
p-type configuration and the other on n-type.Comment: paper submitted for the 2008 Carolina International Symposium on
Neutrino Physic
Astroparticle Physics with a Customized Low-Background Broad Energy Germanium Detector
The MAJORANA Collaboration is building the MAJORANA DEMONSTRATOR, a 60 kg
array of high purity germanium detectors housed in an ultra-low background
shield at the Sanford Underground Laboratory in Lead, SD. The MAJORANA
DEMONSTRATOR will search for neutrinoless double-beta decay of 76Ge while
demonstrating the feasibility of a tonne-scale experiment. It may also carry
out a dark matter search in the 1-10 GeV/c^2 mass range. We have found that
customized Broad Energy Germanium (BEGe) detectors produced by Canberra have
several desirable features for a neutrinoless double-beta decay experiment,
including low electronic noise, excellent pulse shape analysis capabilities,
and simple fabrication. We have deployed a customized BEGe, the MAJORANA
Low-Background BEGe at Kimballton (MALBEK), in a low-background cryostat and
shield at the Kimballton Underground Research Facility in Virginia. This paper
will focus on the detector characteristics and measurements that can be
performed with such a radiation detector in a low-background environment.Comment: Submitted to NIMA Proceedings, SORMA XII. 9 pages, 4 figure
Cytosolic Guanine Nucledotide Binding Deficient Form of Transglutaminase 2 (R580a) Potentiates Cell Death in Oxygen Glucose Deprivation
Transglutaminase 2 (TG2) is a hypoxia-responsive protein that is a calcium-activated transamidating enzyme, a GTPase and a scaffolding/linker protein. Upon activation TG2 undergoes a large conformational change, which likely affects not only its enzymatic activities but its non-catalytic functions as well. The focus of this study was on the role of transamidating activity, conformation and localization of TG2 in ischemic cell death. Cells expressing a GTP binding deficient form of TG2 (TG2-R580A) with high basal transamidation activity and a more extended conformation showed significantly increased cell death in response to oxygen-glucose deprivation; however, targeting TG2-R580A to the nucleus abrogated its detrimental role in oxygen-glucose deprivation. Treatment of cells expressing wild type TG2, TG2-C277S (a transamidating inactive mutant) and TG2-R580A with Cp4d, a reversible TG2 inhibitor, did not affect cell death in response to oxygen-glucose deprivation. These findings indicate that the pro-cell death effects of TG2 are dependent on its localization to the cytosol and independent of its transamidation activity. Further, the conformational state of TG2 is likely an important determinant in cell survival and the prominent function of TG2 in ischemic cell death is as a scaffold to modulate cellular processes
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