Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session U16: Particle Detectors III |
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Sponsoring Units: DPF Chair: Nick Hadley, University of Maryland Room: Key 12 |
Monday, April 13, 2015 3:30PM - 3:42PM |
U16.00001: Development of lithium-loaded liquid scintillator for PROSPECT Danielle Norcini The PROSPECT experiment will use a segmented detector positioned 7-20m from the High Flux Isotope Reactor core to measure the antineutrino spectrum of uranium-235 and perform a sterile neutrino search. Such measurements require the use of liquid scintillator with the capability to distinguish prompt and delayed signals from inverse beta decay events. The characterization of light yield, pulse shape discrimination performance, and neutron capture properties of the lithium-loaded scintillator have been studied with a test detector at Yale. These results will be discussed in the context of their application to antineutrino detection with the PROSPECT experiment. [Preview Abstract] |
Monday, April 13, 2015 3:42PM - 3:54PM |
U16.00002: A 3-D Theoretical Model for Calculating Plasma Effects in Germanium Detectors Wenzhao Wei, Jing Liu, Dongming Mei In the detection of WIMP-induced nuclear recoil with Ge detectors, the main background source is the electron recoil produced by natural radioactivity. The capability of discriminating nuclear recoil (n) from electron recoil ($\gamma )$ is crucial to WIMP searches. Digital pulse shape analysis is an encouraging approach to the discrimination of nuclear recoil from electron recoil since nucleus is much heavier than electron and heavier particle generates ionization more densely along its path, which forms a plasma-like cloud of charge that shields the interior from the influence of the electric field. The time needed for total disintegration of this plasma region is called plasma time. The plasma time depends on the initial density and radius of the plasma-like cloud, diffusion constant for charge carriers, and the strength of electric field. In this work, we developed a 3-D theoretical model for calculating the plasma time in Ge detectors. Using this model, we calculated the plasma time for both nuclear recoils and electron recoils to study the possibility for Ge detectors to realize n/$\gamma $ discrimination and improve detector sensitivity in detecting low-mass WIMPs. [Preview Abstract] |
Monday, April 13, 2015 3:54PM - 4:06PM |
U16.00003: Low-energy recoils and energy scale in liquid xenon detector for direct dark matter searches Lu Wang, Dongming Mei Liquid xenon has been proven to be a great detector medium for the direct search of dark matter. However, in the energy region of below 10 keV, the light yield and charge production are not fully understood due to the convolution of excitation, recombination and quenching. We have already studied a recombination model to explain the physics processes involved in liquid xenon. Work is continued on the average energy expended per electron-ion pair as a function of energy based on the cross sections for different type of scattering processes. In this paper, the results will be discussed in comparison with available experimental data using Birk's Law to understand how scintillation quenching contributes to the non-linear light yield for electron recoils with energy below 10 keV in liquid xenon. [Preview Abstract] |
Monday, April 13, 2015 4:06PM - 4:18PM |
U16.00004: Energy Resolution Optimization of the Yale ``PIXeY'' Two-Phase Xenon Detector Nicholas Destefano, Moshe Gai, Daniel McKinsey, Ethan Bernard, Christopher Wahl, Blair Edwards, Markus Horn, Nicole Larsen, Brian Tennyson PIXeY (Particle Identification in Xenon at Yale) is a two-phase (liquid/gas) xenon prototype detector with 3-kg active mass. The two-phase xenon technology has many applications that include gamma-ray imaging, neutrinoless double beta decay searches, dark matter searches, and 4$\pi $ gamma-ray detectors for studies in Nuclear Astrophysics. PIXeY was built to optimize energy resolution, position resolution, and gamma/neutron discrimination. A number of fiducial cuts and correction factors were used to optimize energy resolution. The light and charge signals were corrected by the spatial location of the event within the detector, taking into account effects such as the electron lifetime, geometric light collection, and any other position and field-dependent variations. The energy spectrum of various sources was studied by varying the cathode, anode, and PMT voltages. Optimal configurations for the drift and scintillation fields were found for energies ranging from 41.5 keV ($^{83m}$Kr) to 2.61 MeV ($^{228}$Th), resolving the light signal and keeping the charge signal unsaturated. In addition, after optimizing for the energy resolution of Cs-137 (662 keV) the value obtained was 1.4{\%} $\sigma $/E. Once the energy resolution studies have concluded, PIXeY will serve as a platform for future improvements, including multiple optical volumes and single-wire readout for R{\&}D on gamma-ray imaging. [Preview Abstract] |
Monday, April 13, 2015 4:18PM - 4:30PM |
U16.00005: The DEAP 3600 Dark Mater Detector Thomas Sonley The DEAP-3600 dark matter detector consists of 3,600 kg of liquid argon contained in an ultra-pure acrylic cryogenic vessel. The experiment is located 2 km underground at SNOLAB. DEAP-3600 is entering the commissioning phase. Scintillation light from events in the detector is observed by 255 high-efficiency room temperature PMTs. Electromagnetic backgrounds, including those from argon-39, are rejected using pulse shape discrimination based on timing. Backgrounds from neutrons and alphas are mitigated by ensuring excellent radiopurity and using a high efficiency neutron shield. The DEAP-3600 background budget is 0.2 events per year allowing a cross-section sensitivity of 10$^{-46}$ cm$^2$ for scattering of Weakly Interacting Massive Particles with a 100-GeV mass in a 3-year run. In this talk, we will describe the status and physics reach, highlighting that it is expected to reach competitive sensitivity within months of the start of data collection. [Preview Abstract] |
Monday, April 13, 2015 4:30PM - 4:42PM |
U16.00006: A p-type point-contact germanium detector with amorphous semiconductor surface Jing Liu, Dongming Mei The p-type point-contact high purity germanium detector is a well-accepted technology in rare-event search experiments due to its ultra-low energy threshold and excellent single/multiple-site event discrimination power. However, there is an about 1~mm thick transient layer below the lithium-diffused n+ outer surface on a traditional p-type germanium detector, where only part of the charges created by an interaction can be collected. Background events located in this layer have their energies misidentified and may contaminate signal regions in rare-event search experiments. In this work, we discuss the possibility to replace the lithium-diffused surface with a 0.1~micron thick amorphous semiconductor one to eliminate the partial-charge-collection layer. Surface and low energy events can be identified by their fully deposited energies together with rise times of their electronic pulses. In addition, the thin surface has the following two advantages over the traditional lithium-diffused one. At first, it maximizes the sensitive volume of the detector. Secondly, it can be segmented easily, providing rich information regarding the interaction topology, which is crucial for background identification in rare-event searches. [Preview Abstract] |
Monday, April 13, 2015 4:42PM - 4:54PM |
U16.00007: Improving axion detection sensitivity in high purity germanium detector based experiments Wenqin Xu, Steven Elliott Thanks to their excellent energy resolution and low energy threshold, high purity germanium (HPGe) crystals are widely used in low background experiments searching for neutrinoless double beta decay, \textit{e.g.} the \textsc{Majorana} \textsc{Demonstrator} and the GERDA experiments, and low mass dark matter, \textit{e.g.} the CDMS and the EDELWEISS experiments. A particularly interesting candidate for low mass dark matter is the axion, which arises from the Peccei-Quinn solution to the strong CP problem and has been searched for in many experiments. Due to axion-photon coupling, the postulated solar axions could coherently convert to photons via the Primakeoff effect in periodic crystal lattices, such as those found in HPGe crystals. The conversion rate depends on the angle between axions and crystal lattices, so the knowledge of HPGe crystal axis is important. In this talk, we will present our efforts to improve the HPGe experimental sensitivity to axions by considering the axis orientations in multiple HPGe crystals simultaneously.\\ [Preview Abstract] |
Monday, April 13, 2015 4:54PM - 5:06PM |
U16.00008: Charge Trapping in Germanium Dark Matter Detectors Arran Phipps Experiments such as CDMS and EDELWEISS operate arrays of high purity germanium detectors in an effort to directly detect dark matter. Discrimination between electron recoil background events and nuclear recoil signal events is performed by the simultaneous measurement of ionization and phonons. The detectors are operated in a unique regime of low temperature ($\sim$50mK) and low electric field ($\sim$V/cm). Both experiments observe a degradation in charge collection efficiency over time, presumed to be due to space charge buildup caused by poorly-understood charge carrier trapping processes, requiring the detectors undergo a periodic reset procedure. We have performed an experiment to measure charge trapping in CDMS detectors as a function of electric field for electrons and holes. We present measured drift velocities and trapping lengths up to fields of $\sim$24V/cm and provide a novel theoretical interpretation which is in good agreement with the data. We discuss the implications of these results for future germanium dark matter detectors. [Preview Abstract] |
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