Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session R12: Dark Matter Instrumentation I |
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Sponsoring Units: DPF DNP Room: Plaza Court 1 |
Monday, April 15, 2013 1:30PM - 1:42PM |
R12.00001: Energy Scales for Nuclear Recoils in CDMS II Silicon and Germanium Detectors Scott Fallows A systematic calibration of the detector response to low-energy nuclear recoils is necessary to translate results from the direct detection of Weakly Interacting Massive Particles (WIMPs) into allowed ranges of WIMP mass and couplings. We present measurements of the energy scale for nuclear recoils for the Z-sensitive Ionization and Phonon (ZIP) detectors used by the Cryogenic Dark Matter Search (CDMS). The absolute energy scale and upper limits on its uncertainty are determined by comparing the observed energy spectra to those expected from detailed Monte Carlo simulations of neutrons incident from a $^{252}$Cf source in calibration runs of the Ge and newly analyzed Si detectors, and cross-checked by comparisons of neutron ionization yields with those measured by other experiments. Implications on WIMP limits are shown. [Preview Abstract] |
Monday, April 15, 2013 1:42PM - 1:54PM |
R12.00002: Underground Performance of SuperCDMS iZIP Detectors Adam Anderson SuperCDMS is currently operating a 10-kg array of cryogenic germanium detectors in the Soudan underground laboratory to search for weakly interacting massive particles, a leading dark matter candidate. These detectors, known as iZIPs, measure both ionization and athermal phonons from particle interactions with multiple sensors on both sides of a Ge crystal. The information from each event provides excellent discrimination between electronic recoils and nuclear recoils, as well as discrimination between events on the detector surface and those in the interior. I will discuss the multiple redundant methods for background rejection in the iZIP, present the background discrimination power that has been demonstrated during underground running in Soudan, and comment on the operational stability and performance of the iZIP. Based on current performance, these detectors are scalable to a 200-kg array proposed for installation in SNOLAB as the next phase of SuperCDMS. [Preview Abstract] |
Monday, April 15, 2013 1:54PM - 2:06PM |
R12.00003: Geant4 Simulations of SuperCDMS iZip Detector Charge Carrier Propagation and FET Readout Rob Agnese The SuperCDMS experiment aims to directly detect dark matter particles called WIMPs (Weakly Interacting Massive Particles). The detectors collect phonon and ionization energy of incident particles for analysis. The SuperCDMS Detector Monte Carlo group is implementing low temperature phonon and ionization simulations in Geant4 in order to study the response of the detectors to incident events. Phonons and electron-hole pairs are tracked in a low temperature crystal detector. The resulting TES phonon readout, as well as the FET charge readout are simulated. The Geant4 framework is well-suited to these tasks. The charge transport in the presence of a complex electric field is performed by calculating a tetrahedral mesh of potentials across the crystal volume. To calculate the FET readout, the Shockley-Ramo theorem is applied to simulate the current in the FET. The focus of this presentation will be on incorporating and using the software package, Qhull, to calculate a tetrahedral mesh from known potentials and then using barycentric coordinates to perform a linear interpolation to calculate the field. After calculating the field at each charge carrier's position, the Shockley-Ramo theorem is applied and the previous triangulation technique is performed to simulate the FET response [Preview Abstract] |
Monday, April 15, 2013 2:06PM - 2:18PM |
R12.00004: Active Neutron Veto Shield Design for SuperCDMS-SNOLAB Hang Qiu Protection against neutron backgrounds is one of the key issues for the next generation SuperCDMS direct dark matter detection experiment that aims at exploring the 10$^{-46}$ cm$^{2}$ cross section region for spin-independent interactions of Weakly Interacting Massive Particles (WIMPs) with nucleons. Estimation of the background from radioactive processes is a crucial task for the current experiment stage and for designing future large-scale detectors. An active neutron veto would make the next generation of dark matter experiment more robust, improving the credibility of a dark matter detection claim based on the observation of a few recoil events. SuperCDMS is investigating the feasibility of adding a liquid scintillator active neutron veto, loaded with high neutron capture cross section isotopes, to the SuperCDMS SNOLAB shield design. This system not only will allow us to reject neutron-induced backgrounds, but also will provide an in-situ measurement of the neutron flux near the detector. I will report the status of ongoing studies related to the design and construction of such a veto. [Preview Abstract] |
Monday, April 15, 2013 2:18PM - 2:30PM |
R12.00005: The LUX Experiment - Detector performance, cryogenics, and controls Patrick Phelps LUX, the Large Underground Xenon experiment, is a 350 kg dual-phase, liquid-gas, xenon TPC designed to directly detect Dark Matter interactions. LUX has completed it's surface run program and underground deployment, expecting WIMP search results in 2013. To ensure quality science data, exacting cryogenic control systems are needed. LUX makes use of a series of thermosyphon and heat exchanger systems to ensure these design goals are met. This talk will review detector cryogenic performance, liquid xenon circulation, and detector monitoring and control systems. [Preview Abstract] |
Monday, April 15, 2013 2:30PM - 2:42PM |
R12.00006: The LUX experiment - TPC design and performance Jeremy Chapman The Large Underground Xenon (LUX) experiment will facilitate direct detection of Weakly Interacting Massive Particles (WIMPs) with a 350 kg xenon TPC (Time Projection Chamber). The LUX TPC is a dual-phase (liquid/gas) detector with a 49 cm drift length, walled by PTFE reflector panels. The active region is observed by 122 photomultiplier tubes, 61 in the top array and 61 in the bottom array. The LUX detector is calibrated using external gamma and neutron sources, and internal calibration lines using activated xenon and Kr-83m. I will discuss the detector design and performance and expected WIMP sensitivity for the upcoming dark matter search. [Preview Abstract] |
Monday, April 15, 2013 2:42PM - 2:54PM |
R12.00007: The LUX experiment - Design and performance of the krypton removal system Chang Lee LUX is an experiment built to detect weakly interacting massive particles as a candidate for cold dark matter using liquid xenon as a target material. Since xenon is a noble gas, a getter is used to remove most impurities. However, noble gas impurities remain, including radioactive krypton and argon isotopes which could dominate the dark matter signal. To remove these contaminants, a chromatographic separation system based on adsorption on activated charcoal was built using helium as a carrier gas. This talk will review the design and performance of the chromatographic system as it processed the LUX xenon stockpile in the fall of 2012. [Preview Abstract] |
Monday, April 15, 2013 2:54PM - 3:06PM |
R12.00008: The LUX experiment - trigger and data acquisition systems Eryk Druszkiewicz The Large Underground Xenon (LUX) detector is a two-phase xenon time projection chamber designed to detect interactions of dark matter particles with the xenon nuclei. Signals from the detector PMTs are processed by custom-built analog electronics which provide properly shaped signals for the trigger and data acquisition (DAQ) systems. During calibrations, both systems must be able to handle high rates and have large dynamic ranges; during dark matter searches, maximum sensitivity requires low thresholds. The trigger system uses eight-channel 64-MHz digitizers (DDC-8) connected to a Trigger Builder (TB). The FPGA cores on the digitizers perform real-time pulse identification (discriminating between S1 and S2-like signals) and event localization. The TB uses hit patterns, hit maps, and maximum response detection to make trigger decisions, which are reached within few microseconds after the occurrence of an event of interest. The DAQ system is comprised of commercial digitizers with customized firmware. Its real-time baseline suppression allows for a maximum event acquisition rate in excess of 1.5 kHz, which results in virtually no deadtime. The performance of the trigger and DAQ systems during the commissioning runs of LUX will be discussed. [Preview Abstract] |
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