Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session M16: Dark Matter II |
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Sponsoring Units: DPF Chair: Josh Klein, University of Pennsylvania Room: 251D |
Sunday, April 17, 2016 3:30PM - 3:42PM |
M16.00001: Detecting dark matter with scintillating bubble chambers Jianjie Zhang, C Eric Dahl, Miaotianzi Jin, Daniel Baxter Threshold based direct WIMP dark matter detectors such as the superheated bubble chambers developed by the PICO experiment have demonstrated excellent electron-recoil and alpha discrimination, excellent scalability, ease of change of target fluid, and low cost. However, the nuclear-recoil like backgrounds have been a limiting factor in their dark matter sensitivity. We present a new type of detector, the scintillating bubble chamber, which reads out the scintillation pulse of the scattering events as well as the pressure, temperature, acoustic traces, and bubble images as a conventional bubble chamber does. The event energy provides additional handle to discriminate against the nuclear-recoil like backgrounds. Liquid xenon is chosen as the target fluid in our prototyping detector for its high scintillation yield and suitable vapor pressure which simplifies detector complexity. The detector can be used as an R&D tool to study the backgrounds present in the current PICO bubble chambers or as a prototype for standalone dark matter detectors in the future. [Preview Abstract] |
Sunday, April 17, 2016 3:42PM - 3:54PM |
M16.00002: Latest Results from the PICO-2L Dark Matter Detector, and the identification and mitigation of particulate-induced backgrounds Daniel Baxter The PICO Collaboration has taken a key step toward a background-free bubble chamber for WIMP dark matter detection. An unexpected background of unknown origin limited WIMP searches in the PICO-2L and PICO-60 detectors at SNOLAB in 2013 and 2014. Recent efforts targeting particulate contamination in the active volume of PICO-2L have reduced this background by at least one order of magnitude, to a rate below the known neutron background in the detector. The resulting data set the most stringent limit to date from a direct detection experiment on spin-dependent WIMP-proton interactions. I will present a comparison of the background-limited Run-1 of PICO-2L with the new results from Run-2, identifying particulate as the primary source of the previously unexplained background. I will describe the engineering and operational controls now being implemented to eliminate this background in the PICO-60 detector, with the goal of a background-free run using our large detector within the next year. [Preview Abstract] |
Sunday, April 17, 2016 3:54PM - 4:06PM |
M16.00003: Calibration of PICO Bubble Chamber Dark Matter Detectors Miaotianzi Jin The PICO Collaboration builds bubble chambers for the direct detection of WIMP dark matter. I will present the suite of calibration experiments performed to measure the sensitivity of these chambers to nuclear recoils (the expected WIMP signal) and to gamma rays (a common background to the WIMP signal). These calibrations include measurements with a 10-ml C3F8 bubble chamber at Northwestern University and with a 30-ml C3F8 bubble chamber deployed in the University of Montreal's tandem Van de Graaf facility, giving the bubble chamber response to a variety of gamma rays, broad-spectrum neutron sources, and mono-energetic low energy neutrons. I will compare our measured sensitivities to those predicted by a simple thermodynamic model and will show how the results impact our ability to detect dark matter, with a focus on light WIMP searches. [Preview Abstract] |
Sunday, April 17, 2016 4:06PM - 4:18PM |
M16.00004: Search for Annual Modulation in CDMS II Danielle Speller Weakly Interacting Massive Particles (WIMPs) are one of the leading candidates for the undetected mass component comprising $\sim$27\% of the observable universe. An excess in the nuclear-recoil event rate measured by a detector, combined with an annual periodicity introduced by the revolution of the Earth about the Sun, is an important indicator of the direct detection of particle dark matter. The Cryogenic Dark Matter Search (CDMS) experiment uses semiconductor crystals to search for WIMPs scattering from atomic nuclei through the simultaneous measurement of ionization and athermal phonons. This technique has achieved excellent discrimination between nuclear recoils (expected for WIMP interactions) and radioactively induced electron recoils, enabling a sensitive search for an annually modulating signal. I will discuss updated results of this search, including possible systematic effects, and describe implications for interpretations of other experimental results such as those from the CoGeNT experiment. [Preview Abstract] |
Sunday, April 17, 2016 4:18PM - 4:30PM |
M16.00005: Radon Mitigation for the SuperCDMS-SNOLAB Dark Matter Experiment Joseph Street Experiments that seek to detect very rare processes, such as interactions of the dark matter particles thought to make up 85\% of the mass of the universe, may suffer background interactions from radon daughters that have plated out onto detector surfaces. To reduce these backgrounds, an ultra-low-radon cleanroom was built at the South Dakota School of Mines \& Technology. Cleanroom air is supplied by an optimized vacuum-swing-adsorption radon mitigation system that has achieved a $> 300\times$ reduction from an input activity of 58.6 $\pm$ 0.7 Bq/m$^{3}$ to a cleanroom activity of 0.13 $\pm$ 0.06 Bq/m$^{3}$. Expected backgrounds due to radon daughters for the SuperCDMS dark matter search will be presented. [Preview Abstract] |
Sunday, April 17, 2016 4:30PM - 4:42PM |
M16.00006: The Search for High Mass WIMPs with the SuperCDMS Experiment Hang Qiu About 26.8{\%} of the universe mass is contributed from dark matter. Weakly Interacting Massive Particle(WIMP) is currently the most promising dark matter candidate. SuperCDMS is one of the leading direct dark matter detection experiments around the world. Its biggest goal is to use semiconductor detectors under the cryogenic condition to detect WIMPs. Both ionization and phonon signals are read out via our detector sensors during the operation periods. The high threshold analysis aims to search for high mass WIMPs based on the data collected in a 2-year-long period of time from the SuperCDMS experiment setup located at the Soudan mine in Minnesota. In today's presentation, I am going to talk about the approaches towards this goal. [Preview Abstract] |
Sunday, April 17, 2016 4:42PM - 4:54PM |
M16.00007: Controlling cosmogenic radioactivity in SuperCDMS SNOLAB Alan Robinson The SuperCDMS SNOLAB experiment is being designed with sensitivity far in excess of existing experiments to low-mass WIMP dark matter. To attain this sensitivity, events due to ionizing radiation that mimic dark matter must be controlled. Depending on the source of ionizing radiation, different strategies are required for its mitigation. Cosmic rays and neutron radiation at earth's surface continuously generate an multitude of radioactive atoms in the materials that will be used to build SuperCDMS SNOLAB. Of these isotopes, we are concerned with isotopes with long half-lives and high production rates. The production and effects of cobalt-60, silicon-32, and tritium will be discussed. A new analysis of the silicon-32 concentration in the CDMS-II silicon detectors will be discussed and compared to the measured concentration of silicon-32 in the silicon used by the DAMIC dark matter search. [Preview Abstract] |
Sunday, April 17, 2016 4:54PM - 5:06PM |
M16.00008: The MiniCLEAN Experiment Christopher Jackson The MiniCLEAN (Cryogenic Low-Energy Astrophysics with Noble liquids) detector is a prototype experiment in the search for weakly interacting massive particle dark matter. A target of single phase liquid argon with a fiducial mass of 150 kg is being deployed in a spherical detector surrounded by cryogenic temperature photomultiplier tubes. This design maximizes light yield and allows pulse shape discrimination to be used to separate nuclear recoils from electron recoil background events. The detector will demonstrate the technologies necessary for a future generation dark matter and low energy solar neutrino experiment using, interchangeably, targets of argon and neon. This talk will summarize the status of the ongoing commissioning and first physics runs at SNOLAB in Sudbury, Canada [Preview Abstract] |
Sunday, April 17, 2016 5:06PM - 5:18PM |
M16.00009: Informing Next Generation Dark Matter and Neutrino Detector Designs with MiniCLEAN Christopher Benson Single phase, zero field, liquid noble gas scintillator detectors are a simple, scalable and cost effective approach for dark matter and neutrino detection. The operation of MiniCLEAN, a dark matter detector currently commissioning with a liquid argon target at SNOLAB in Canada, will help inform the design of a future multi-ton experiment. The technical objectives of MiniCLEAN\^{a}\texteuro \texttrademark s role as a technology demonstrator will be discussed.A key enabling technology for many detectors is the use of the common wavelength shifting medium Tetraphenyl Butadiene (TPB). Thin films of TPB are used to shift ultraviolet scintillation light into the visible spectrum for detection and event reconstruction. The wavelength shifting (WLS) efficiency and emission spectrum has been previously measured down to 120 nm. To build liquid noble gas scintillator detectors with lighter elements (Ne, He) that use TPB as a WLS medium, the wavelength shifting efficiency must be known closer to 80 nm. The current status and preliminary results of wavelength shifting efficiency measurements down to 45nm will also be presented. [Preview Abstract] |
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