Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session CG: Mini-symposium on Identifying Dark Matter I: Direct Detection of WIMP Dark Matter |
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Sponsoring Units: DNP Chair: Andrew Hime, Los Alamos National Laboratory Room: Gaylord Opryland Hermitage D |
Friday, October 27, 2006 9:00AM - 9:36AM |
CG.00001: Direct Detection of WIMP Dark Matter Invited Speaker: Astrophysical observations indicate that about 80\% of the mass of the universe is in the form of non-baryonic particles beyond the standard model of particle physics. One exciting and well motivated candidate is weakly interacting massive particles (WIMPs) left over from the Big Bang. Direct detection of these particles requires sophisticated detectors to defeat much higher-rate backgrounds due to radioactivity and other sources. Promising techniques identify individual interactions in shielded fiducial volumes and distinguish nuclear-recoil signal candidates from electron-recoil backgrounds, based on the timing, energy density, and/or the division of the energy into signals of ionization, scintillation, or phonons. I will review the techniques of the dozens of experiments searching for WIMPs and summarize the most interesting results of experiments not being discussed in greater detail at this symposium. [Preview Abstract] |
Friday, October 27, 2006 9:36AM - 9:48AM |
CG.00002: The Cryogenic Dark Matter Search II: Current Run Status Angela Reisetter The CDMSII experiment has proven the merits of using germanium crystals and tungsten transition-edge sensors in searching for dark matter WIMPs, obtaining the world's most sensitive upper limits on the WIMP-nucleon cross-section of 1.6x10$^{-43}$ cm$^{2}$ from its exposure of twelve detectors (1.5 kg Ge) in 2004. These ZIP (Z(depth)-sensitive Ionization and Phonon) detectors use phonon and ionization measurements to discriminate between electron-recoil backgrounds and nuclear-recoil signal. Currently in the Soudan Underground Laboratory, twenty-nine detectors (4.5 kg Ge) have been commissioned and are taking data. This talk will focus on the current run, including operational improvements, calibrations, and overall data quality and detector performance. [Preview Abstract] |
Friday, October 27, 2006 9:48AM - 10:00AM |
CG.00003: SuperCDMS: Taking Cryogenic Dark Matter Search Techniques to 25kg and Beyond Michael Dragowsky The CDMS\ II experiment has demonstrated the merits of using athermal phonon signatures in single-crystal semiconductor detectors to search for dark matter in the form of weakly-interacting massive particles (WIMPs), obtaining the world's most sensitive upper limits on the WIMP-nucleon cross section of $1.6\times10^{-43} \mathrm{cm}^2$ (60 GeV/$c^2$ WIMP) from its exposure of twelve detectors (1.5 kg Ge and 0.6 kg Si) in 2004. The SuperCDMS Collaboration will extend our strategy to perform zero-background experiments featuring progressively larger target mass for WIMP direct detection. The next stage experiment will employ enhanced CDMS~II-style detectors, and improved analysis techniques to achieve 10$^{-45} \mathrm{cm}^2$ sensitivity using 25 kg of Ge-based detectors. Such sensitivity in a direct detection dark matter experiment is of great interest for particle physics, astrophysics and cosmology. The design changes and performance obtained from the enhanced detectors, and the current understanding of background levels and rejection techniques applicable to SuperCDMS~25-kg will be reported. Prospects to further improve background rejection through advances in detector design and consideration of the needs to industrialize our fabrication methods will outlined. [Preview Abstract] |
Friday, October 27, 2006 10:00AM - 10:12AM |
CG.00004: Zeplin II Status Update Weichung Ooi, Hanguo Wang, David Cline, Peter Smith We discuss the design, underground performance and current status of 32 kg Zeplin II two phase detector. Zeplin II is designed to observe low energy nuclear recoil events from hypothetical weakly interacting massive particles (WIMP). The detector records two signals from each event - the direct scintillation signal S1 in Xe liquid, followed by ionization signal S2 produced by ionization electron in gas phase via electroluminescence. The ratio of S1 and S2 discriminates nuclear recoils events from gamma recoil events. [Preview Abstract] |
Friday, October 27, 2006 10:12AM - 10:24AM |
CG.00005: The XENON Dark Matter Experiment: Status of the XENON10 Phase. Maria Elena Monzani The XENON experiment searches for Weakly Interacting Massive Particles (WIMPs) with liquid xenon (LXe) as the active target. The detector is a 3-D position sensitive Time Projection Chamber optimized to simultaneously measure the ionization and scintillation produced by a recoil event down to energies of 16 keV. The distinct ratio of the two signals for nuclear recoils arising from WIMPs and neutrons and for electron recoils from the dominant gamma-ray background determines its event-by-event discrimination. With 1 ton of LXe distributed in ten identical modules, the proposed XENON1T will achieve a sensitivity more than a factor of thousand beyond current limits. A phased program will test the 10 kg target (XENON10) followed by a 100 kg (XENON100) module. The XENON10 detector was assembled and preliminarily tested at Columbia in January 2006. It was shipped to the Gran Sasso National Laboratory in March and then installed in the underground lab. Testing and calibration runs have been performed through June, while the shielding was constructed: the detector was moved in its final location in the shielded environment in July. The first XENON10 physics run will begin in summer 2006. I present the status of this experiment, along with its expected performance and sensitivity. [Preview Abstract] |
Friday, October 27, 2006 10:24AM - 10:36AM |
CG.00006: The WARP program for Direct WIMP Dark Matter Search Cristiano Galbiati The WARP detector is characterized by a unique technology for the identification of nuclear recoils, eventually induced by WIMPs' interactions with argon. The detection technique takes advantage of a double discrimination between argon recoils and gamma or beta induced background, providing a discrimination power against betas potentially in excess of one event over 10$^{8}$. The 100 liter (140 kg) detector, presently under construction and to be commissioned during the second half of 2006, will be also equipped with an active shield for identification and rejection of neutron induced recoils. A 2.3 liter volume prototype (3 kg active mass, 1.8 kg fiducial mass) is installed in Gran Sasso since May 2004 and was run underground in several operating conditions: with and without gamma shielding, with and without neutron shielding. Our measurements confirm the discrimination power indicated above. I will present results on the characterization of the background. I will also present results of a run for direct search of WIMP Dark Matter, with the complete neutron and gamma shielding, in which a total exposure of about 100 kg$\cdot $day was accumulated. [Preview Abstract] |
Friday, October 27, 2006 10:36AM - 10:48AM |
CG.00007: Dark matter Experiment with Argon and Pulse shape discrimination (DEAP) Keith Rielage The Dark matter Experiment with Argon and Pulse shape discrimination (DEAP) exploits pulse-shape discrimination of scintillation light in liquid argon to provide background reduction required for a sensitive dark matter search. Currently, a 7-kg detector has been built (DEAP-1) and is being commissioned this fall at SNOLAB. A summary of the design of the detector and current status will be presented with emphasis on backgrounds to the dark matter search. Prospects of scaling this technology up in size to a future one ton detector will be discussed. [Preview Abstract] |
Friday, October 27, 2006 10:48AM - 11:00AM |
CG.00008: Dark matter and mini-CLEAN James Nikkel, Hugh Lippincott, Daniel McKinsey, Andrew Hime, Dongming Mei, Keith Rielage, Laura Stonehill, Ed Kearns, Dan Gastler, Kevin Coakley, Mark Boulay Because liquid neon is easily purified, has no intrinsic radioactivity, and scintillates brightly in response to ionizing radiation, it is a promising material for the detection of rare low-energy events. The mini-CLEAN experiment will contain on active mass of approximately 100 kg of liquid neon viewed by 32 photomultiplier tubes and will serve as a prototype for the 10-100 ton CLEAN detector. Mini-CLEAN will be used to test the practicality of liquid neon as a scintillation material for neutrino detection. Additionally, the liquid neon can be replaced with liquid argon to provide improved sensitivity to dark matter in the form of weakly interacting massive particles. The ability to exchange the two cryogens, with different sensitivities to dark matter and fast neutrons, will allow the two event types to be accurately characterized. Radioactive backgrounds from gamma rays will be rejected through pulse-shape discrimination, which has been shown to be highly efficient in both liquid neon and liquid argon. [Preview Abstract] |
Friday, October 27, 2006 11:00AM - 11:12AM |
CG.00009: Depth \& Shielding Requirements for mini-CLEAN Dong-Ming Mei, Andrew Hime Neutron-induced nuclear recoil represents an irreducible background in detectors aimed at the direct detection of WIMP dark matter. Muon-induced neutrons can be adequately suppressed by staging experiments sufficiently deep underground, however, it is also critical to suppress neutron production via (alpha, n) interactions due to naturally occurring radioactivity in detector construction materials. We present the results of simulations for the mini-CLEAN detector under development to search for WIMP dark matter using 100 kg of liquid argon or liquid neon as the target material. We show that neutron backgrounds can be sufficiently suppressed in a conceptually simple detector using the coincidence between the prompt nuclear recoil signal and the delayed neutron capture gamma ray. The shielding of ($\alpha$,n) neutrons that are produced in rock as a function of thickness of polyethylene is modeled. [Preview Abstract] |
Friday, October 27, 2006 11:12AM - 11:24AM |
CG.00010: A Bubble Chamber for Dark Matter Detection: The COUPP Project Brian Odom Heavy-liquid bubble chambers can be made stable-enough to be used in WIMP searches. Advantages of this approach are an optimal choice of target (CF3I, maximally sensitive to both spin-dependent and -independent WIMP interactions), low cost, good scalability, room temperature operation, extraordinary intrinsic rejection of minimum-ionizing backgrounds (rejection $> 10^9$, as opposed to $\sim$$10^4$ in cryogenic devices), and a number of features permitting rejection of irreducible neutron backgrounds. Scalability to a ton-level mass also appears quite promising. A 2 kg prototype chamber has been constructed and is currently operating at a depth of 300 m.w.e. (meters water equivalent) in the NuMi gallery of Fermilab. The currently observed event rate, believed to be from alpha backgrounds, is expected to yield the best limits on WIMP-proton spin-dependent coupling. A 20 kg modular chamber, expected to have substantially reduced alpha backgrounds, is currently under construction and is expected to yield extremely competitive spin-independent coupling results. [Preview Abstract] |
Friday, October 27, 2006 11:24AM - 11:36AM |
CG.00011: Two-Component Dark Matter in UED Models Ken Hsieh, Rabindra Mohapatra, Salah Nasri We show that in a class of universal extra dimension models (UED), which solves both the neutrino mass and proton decay problem, an admixture of KK photon and KK right handed neutrinos can provide the required amount of cold dark matter (CDM). This model has two parameters $R^{-1}$ and $M_{Z'}$ ($R$ is the radius of the extra space dimensions and $Z'$ the extra neutral gauge boson of the model). Using the value of the relic CDM density, combined with the results from the cryogenic searches for CDM, we obtain upper limits on $R^{-1}$ of about $400-650$ GeV and $M_{Z'}\leq 1.5$ TeV, both being accessible to LHC and a lower bound on the dark matter- nucleon scattering cross section of $10^{-44}$ cm$^2$, which can be probed by the next round of dark matter search experiments. [Preview Abstract] |
Friday, October 27, 2006 11:36AM - 11:48AM |
CG.00012: Status of the DRIFT-II Directional Dark Matter Detector Chamkaur Ghag DRIFT is a directional dark matter detection programme that utilises the fact that as the Earth rotates and revolves around the Sun, an annual and diurnal signal modulation could be detected as a result of relative motion between the Earth and the non-rotating WIMP halo. This would provide very strong evidience of WIMPs since such a signal could not be mimicked by background sources. DRIFT II is an array of gas filled time projection chambers (TPCs) with Multi Wire Proportional Counter (MWPC) readout. Signals from different types of events differ greatly, between nuclear and electron recoils for example, due to the amount of ionisation initially produced and recombination times. This provides phenomenal discrimination capabilities. The first module of the DRIFT-II detector was successfully installed underground at Boulby Mine, N. Yorkshire early last year and has proven very stable, collecting high quality calibration and WIMP data. Since then a second module has been installed and is also currently operational. This presentation will describe the status of the detector and will focus on the determination of neutron efficiency and gamma rejection factors. [Preview Abstract] |
Friday, October 27, 2006 11:48AM - 12:00PM |
CG.00013: Future Techniques for WIMP Astronomy C.J. Martoff, Michael Hosack, Jan Masouh This miniconference title appropriately focusses attention on the crucial problem of {\em identification} of dark matter; how to associate signals in direct detection experiments with galactic halo WIMPs. Spergel, Freese and others long ago pointed out the strong directional anisotropy of WIMP recoils which provides an unambiguous identification signature. Such anisotropy (present in almost any halo model) will rotate in the lab at the sidereal rate, distinguishing it from all terrestrial backgrounds. The author's Negative Ion TPC (NITPC) method allows low-pressure, high field TPC's to be built with 100's of kg of active gas target, and with the high spatial resolution to measure WIMP recoil tracks directionally. DRIFT I, in which the author was a principal investigator, was the first example. Further developments toward practical construction of 100 kg and larger NITPC will be presented here. Topics will include: proven, low channel-count readouts allowing 3-D tracking in these low-occupancy experiments; reconstruction algorithms and simulations of response to several halo models; and work in progress on alternative negative ion formation agents and on new veto detection media. Finally, a fieldable design for an NITPC array made of modules each having $\sim$10 kg active mass will be discussed. [Preview Abstract] |
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