Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session G9: Dark Matter II |
Hide Abstracts |
Sponsoring Units: DPF Chair: Carter Hall, University of Maryland Room: Maryland A |
Sunday, February 14, 2010 8:30AM - 8:42AM |
G9.00001: MiniCLEAN- A Dark Matter Experiment: Overview and Status Kimberly Palladino MiniCLEAN is a direct dark matter detection experiment currently under construction at SNOLab. It will utilize ~500 kg of liquid cryogen with a fiducial volume over 150 kg. Detection requires seeing a low energy nuclear recoil event in the single-phase target material. This is interchangeable between argon and neon, as they provide different responses to signal and background. MiniCLEAN's spherical geometry and modular design maximize light yield with cold photomultiplier tubes. Pulse shape discrimination will be used to separate electron recoil backgrounds from nuclear recoil signals, while efforts against radon contamination and shielding mitigate the troublesome neutron scattering events which mimic a dark matter signal. The design, projected sensitivity, assembly status and schedule will be presented. [Preview Abstract] |
Sunday, February 14, 2010 8:42AM - 8:54AM |
G9.00002: ShellFit: Reconstruction in the MiniCLEAN Detector Stanley Seibert The MiniCLEAN dark matter experiment is an ultra-low background liquid cryogen detector with a fiducial volume of approximately 150 kg. Dark matter candidate events produce ultraviolet scintillation light in argon at 128 nm and in neon at 80 nm. In order to detect this scintillation light, the target volume is enclosed by acrylic plates forming a spherical shell upon which an organic fluor, tetraphenyl butadiene (TPB), has been applied. TPB absorbs UV light and reemits visible light isotropically which can be detected by photomultiplier tubes. Two significant sources of background events in MiniCLEAN are decays of radon daughters embedded in the acrylic surface and external sources of neutrons, such as the photomultiplier tubes themselves. Both of these backgrounds can be mitigated by reconstructing the origin of the scintillation light and cutting events beyond a particular radius. The scrambling of photon trajectories at the TPB surface makes this task very challenging. The ``ShellFit'' algorithm for reconstructing event position and energy in a detector with a spherical wavelength-shifting shell will be described. The performance of ShellFit will be demonstrated using Monte Carlo simulation of several event types in the MiniCLEAN detector. [Preview Abstract] |
Sunday, February 14, 2010 8:54AM - 9:06AM |
G9.00003: Calibration of the MiniCLEAN detector Michael Akashi-Ronquest The DEAP/CLEAN collaboration is constructing MiniCLEAN, a single-phase noble-liquid dark matter experiment with a projected sensitivity to the spin-independent WIMP-nucleon cross-section of roughly $2 \times 10^{-45} \ \mathrm{cm}^{2}$ for $M_{\mathrm{WIMP}}$ $\approx$ $100 \ \mathrm{GeV}$. The low background nature of MiniCLEAN, coupled with its monolithic self-shielding liquid argon target, makes calibration of the detector a challenge. The MiniCLEAN calibration system will probe the detector's response using external $\gamma$ and neutron sources. Light sources will be utilized to further understand the optical response of the detector. Radioisotope spikes will circumvent self-shielding for low energy calibration, and will also enable dedicated demonstration of argon pulse-shape discrimination using greatly increased amounts of $^{39}$Ar. In addition to probing 3D position and energy reconstruction in MiniCLEAN, the calibration system will also mimic many of the expected backgrounds. [Preview Abstract] |
Sunday, February 14, 2010 9:06AM - 9:18AM |
G9.00004: An active veto for the MiniCLEAN dark matter direct detection search Stephen Jaditz The MiniCLEAN active veto shield is a large water tank surrounding the liquid cryogen dark matter detector located at SNOLAB (6000 mwe depth). The tank is instrumented to detect Cherenkov light from cosmic-ray muons, which produce high-energy spallation neutrons. A fraction of these neutrons can penetrate the water shield and the shielding liquid cryogen and reach the fiducial region of the detector. Such neutrons constitute a background to a dark matter signal. The design and simulation of the veto will be discussed in the context of its impact on MiniCLEAN's dark matter sensitivity. [Preview Abstract] |
Sunday, February 14, 2010 9:18AM - 9:30AM |
G9.00005: Searching for Axion Dark Matter with the ADMX experiment G. Carosi, S.J. Asztalos, R. Bradley, C. Hagmann, J. Hoskins, M. Hotz, J. Hwang, D. Kinion, L. Rosenberg, G. Rybka, P. Sikivie, D.B. Tanner, K. van Bibber Axions are hypothetical pseudoscalar particles that exist as a consequence of the Peccei-Quinn solution to the strong-CP problem. Light axions ($\mu$eV-meV) are also a natural cold dark matter candidate and may be detected by their resonant conversion to microwave photons in a high-Q cavity immersed in a strong magnetic field. This detection strategy provides the basis for the Axion Dark Matter eXperiment (ADMX) which has been taking data at Lawrence Livermore National Laboratory (LLNL) for over a decade. In this experiment, the signal from the cavity is amplified by an ultralow noise amplifier, and mixed down to the audio frequency range in a double-heterodyne receiver. The signal is digitized and a Fourier transform produces a power spectrum, in which the axion would appear as a narrow line at $f=m_ac^2/h$. This talk will present an overview of ADMX, with particular attention to the successful implementation of new ultralow-noise first stage cryogenic SQUID amplifiers, and the first results from this new configuration. [Preview Abstract] |
Sunday, February 14, 2010 9:30AM - 9:42AM |
G9.00006: Limits on thermally-distributed halo dark-matter axions from ADMX Michael Hotz, S.J. Asztalos, R. Bradley, G. Carosi, C. Hagmann, J. Hoskins, J. Hwang, D. Kinion, L. Rosenberg, G. Rybka, P. Sikivie, D.B. Tanner, K. van Bibber The Axion Dark Matter eXperiment (ADMX) at Lawrence Livermore National Laboratory searches for dark-matter axions through their Primakoff conversion to microwave photons in a strong magnetic field, resonantly enhanced by a high-Q cavity. The ADMX medium resolution analysis assumes that halo axions are thermalized with the local virial velocity of the Milky Way, about $270 \frac{km}{sec}$, which implies a spectral line-broadening of one part per million. ADMX has set limits on halo axions for the KSVZ model from $1.6 eV$ to $3.6 eV$. The experiment is the most sensitive spectral receiver in the world, able to detect signals from $400MHz$ to $900MHz$ well below a yoctowatt. This talk will outline the experimental technique, data analysis and results for the medium-resolution search. [Preview Abstract] |
Sunday, February 14, 2010 9:42AM - 9:54AM |
G9.00007: Initial Results from a SQUID-Based High Resolution Axion Search J. Hoskins, S. J. Asztalos, R. Bradley, G. Carosi, D. Goffredo, C. Hagmann, M. Hotz, J. Hwang, D. Kinion, L. Rosenberg, G. Rybka, P. Sikivie, D.B. Tanner, K. van Bibber The Axion Dark Matter eXperiment (ADMX) searches for halo axions via their resonant conversion to microwave photons in a high-Q cavity permeated by a strong magnetic field. Whereas fully thermalized axions would appear in the medium resolution spectrum as a line broadened to one part in a million in frequency (and thus energy), populations of axions characterized by low velocity dispersion could be detected by ADMX in its high resolution channel as sharp lines several orders of magnitude more narrow yet. In this talk, we present a preliminary high-resolution analysis with a frequency resolution of 10 Hz in the 800 MHz range (3.3 microelectronvolt), recently covered with the new SQUID amplifiers. A more sophisticated higher resolution examination will be forthcoming which will need to address the daily and annual modulations to the axion signal due the motion of the Earth. [Preview Abstract] |
Sunday, February 14, 2010 9:54AM - 10:06AM |
G9.00008: Exotic Light Particle Searches with ADMX Gray Rybka, S.J. Asztalos, R. Bradley, G. Carosi, C. Hagmann, J. Hoskins, M. Hotz, J. Hwang, D. Kinion, L. Rosenberg, P. Sikivie, D.B. Tanner, K. van Bibber The ADMX experiment searches for dark matter axions converting to microwave photons via a resonantly-enhanced Primakoff interaction. However, the ADMX setup also has the potential to be sensitive to a host of other light beyond-Standard Model particles. Examples of these are scalar chameleons, which may play a role in dark energy, and hidden sector photons, a common feature of many Standard Model extensions. The results of a search for scalar chameleons using ADMX and plans for a two cavity hidden sector photon search will be presented. [Preview Abstract] |
Sunday, February 14, 2010 10:06AM - 10:18AM |
G9.00009: Gas phase R\&D for the Enriched Xenon Observatory Christina Hagemann The EXO (Enriched Xenon Observatory) collaboration will search for neutrinoless double beta decay using Xe-136. A liquid-phase prototype, EXO-200, is currently being commissioned and will use 80\% enriched Xe-136 to reach an expected sensitivity of the double beta decay mass of approximately 150 meV. Complimentary efforts are underway to explore a gas phase detector option. The current status of the EXO gas phase, which is studying the use of Micromegas and electroluminescence techniques, will be presented. Progress towards a gas phase prototype, which will be used to evaluate the ultimate energy resolution and track reconstruction achievable for 1 MeV electrons, will be shown. [Preview Abstract] |
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