89 research outputs found
Low-Mass WIMP Sensitivity and Statistical Discrimination of Electron and Nuclear Recoils by Varying Luke-Neganov Phonon Gain in Semiconductor Detectors
Amplifying the phonon signal in a semiconductor dark matter detector can be
accomplished by operating at high voltage bias and converting the electrostatic
potential energy into Luke-Neganov phonons. This amplification method has been
validated at up to |E|=40V/cm without producing leakage in CDMSII Ge detectors,
allowing sensitivity to a benchmark WIMP with mass = 8GeV and cross section
1.8e-42cm^2 assuming flat electronic recoil backgrounds near threshold.
Furthermore, for the first time we show that differences in Luke-Neganov gain
for nuclear and electronic recoils can be used to discriminate statistically
between low-energy background and a hypothetical WIMP signal by operating at
two distinct voltage biases. Specifically, 99% of events have p-value<1e-8 for
a simulated 20kg-day experiment with a benchmark WIMP signal with mass =8GeV
and cross section =3.3e-41cm^2.Comment: 6 pages, 5 figures To be published in Journal of Low Temperature
Physic
Temperature Sensitivity of Surface Channels on High-Purity Germanium Detectors
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Determining the Drift Time of Charge Carriers in P-Type Point-Contact HPGe Detectors
An algorithm to measure the drift time of charge carriers in p-type point
contact (PPC) high-purity germanium (HPGe) detectors from the signals processed
with a charge-sensitive preamplifier is introduced. It is demonstrated that the
drift times can be used to estimate the distance of charge depositions from the
point contact and to characterize losses due to charge trapping. A correction
for charge trapping effects over a wide range of energies is implemented using
the measured drift times and is shown to improve the energy resolution by up to
30%.Comment: 16 pages, 8 figures, submitted to Nucl. Instrum. Meth.
Phonon Pulse Shape Discrimination in SuperCDMS Soudan
SuperCDMS is the next phase of the Cryogenic Dark Matter Search experiment,
which measures both phonon and charge signals generated by particle recoils
within a germanium target mass. Charge signals are employed both in the
definition of a fiducial volume and in the rejection of electron recoil
background events. Alternatively, phonons generated by the charge carriers can
also be used for the same two goals. This paper describes preliminary efforts
to observe and quantify these contributions to the phonon signal and then use
them to reject background events. A simple analysis using only one pulse shape
parameter shows bulk electron recoil vs. bulk nuclear recoil discrimination to
the level of 1:10^3 (limited by the statistics of the data), with little
degradation in discrimination ability down to at least 7 keV recoil energy.
Such phonon-only discrimination can provide a useful cross-check to the
standard discrimination methods, and it also points towards the potential of a
device optimized for a phonon-only measurement.Comment: Low Temperature Detector 14 conference proceedings, to be published
in a special issue of the Journal of Low Temperature Physic
A focal plane detector design for a wide-band Laue-lens telescope
The energy range above 60 keV is important for the study of many open
problems in high energy astrophysics such as the role of Inverse Compton with
respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in
SNR, the study of the high energy cut-offs in AGN spectra, and the detection of
nuclear and annihilation lines. Recently the development of high energy Laue
lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a
Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of
celestial sources. The required focal plane detector should have high detection
efficiency over the entire operative range, a spatial resolution of about 1 mm,
an energy resolution of a few keV at 500 keV and a sensitivity to linear
polarization. We describe a possible configuration of the focal plane detector
based on several CdTe/CZT pixelated layers stacked together to achieve the
required detection efficiency at high energy. Each layer can operate both as a
separate position sensitive detector and polarimeter or work with other layers
to increase the overall photopeak efficiency. Each layer has a hexagonal shape
in order to minimize the detector surface required to cover the lens field of
view. The pixels would have the same geometry so as to provide the best
coupling with the lens point spread function and to increase the symmetry for
polarimetric studies.Comment: 10 pages, 9 figure
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
The Majorana Demonstrator readout electronics system
The Majorana Demonstrator comprises two arrays of high-purity germanium detectors constructed to search for neutrinoless double-beta decay in 76Ge and other physics beyond the Standard Model. Its readout electronics were designed to have low electronic noise, and radioactive backgrounds were minimized by using low-mass components and low-radioactivity materials near the detectors. This paper provides a description of all components of the Majorana Demonstrator readout electronics, spanning the front-end electronics and internal cabling, back-end electronics, digitizer, and power supplies, along with the grounding scheme. The spectroscopic performance achieved with these readout electronics is also demonstrated
The Majorana Demonstrator: Progress towards showing the feasibility of a tonne-scale 76Ge neutrinoless double-beta decay experiment
The Majorana Demonstrator will search for the neutrinoless double-beta decay (0vββ) of the 76Ge isotope with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate the neutrino is its own anti-particle, demonstrate that lepton number is not conserved, and provide information on the absolute mass-scale of the neutrino. The Demonstrator is being assembled at the 4850 foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be contained in a low-background environment and surrounded by passive and active shielding. The goals for the Demonstrator are: demonstrating a background rate less than 3 t-1 y-1 in the 4 keV region of interest (ROI) surrounding the 2039 keV 76Ge endpoint energy; establishing the technology required to build a tonne-scale germanium based double-beta decay experiment; testing the recent claim of observation of 0vββ [1]; and performing a direct search for light WIMPs (3-10 GeV/c2)
Characteristics of signals originating near the lithium-diffused N+ contact of high purity germanium p-type point contact detectors
A study of signals originating near the lithium-diffused n+ contact of p-type point contact (PPC) high purity germanium detectors (HPGe) is presented. The transition region between the active germanium and the fully dead layer of the n+ contact is examined. Energy depositions in this transition region are shown to result in partial charge collection. This provides a mechanism for events with a well defined energy to contribute to the continuum of the energy spectrum at lower energies. A novel technique to quantify the contribution from this source of background is introduced. Experiments that operate germanium detectors with a very low energy threshold may benefit from the methods presented herein
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