Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session I7: Astroparticle Physics I |
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Sponsoring Units: DAP Chair: Ulisse Bravar, University of New Hampshire Room: Hyatt Regency Dallas Pegasus A |
Sunday, April 23, 2006 10:30AM - 10:42AM |
I7.00001: Signals in the Co-annihilation Region of Supersymmetry Richard Arnowitt, Adam Aurisano, Bhaskar Dutta, Teruki Kamon, Paul Simeon, David Toback, Peter Wagner, Nikolay Kolev An unanswered problem in physics is the identity of the cold dark matter (CDM) in the universe. One of the leading candidates is a supersymmetric (SUSY) particle, the lightest neutralino. Recent cosmological measurements by the WMAP experiment have tightly constrained the SUSY parameter space in the mSUGRA model to the so called ``co-annihilation'' region in which the lightest supersymmetric tau lepton and the lightest neutralino are nearly degenerate in mass. We examine the prospects of using LHC detectors to measure this mass difference and present preliminary results. [Preview Abstract] |
Sunday, April 23, 2006 10:42AM - 10:54AM |
I7.00002: A new procedure to distinguish between dark energy models and modified gravity models. Mustapha Ishak, Amol Upadhye, David Spergel The acceleration of the expansion of the universe is one of the most important and challenging problems in physics. It is important to determine if the cosmic acceleration is due to a dark energy component in the universe or if it is due to a modification in the gravity sector. We report here results on a procedure that we proposed recently and that will allow one to make such a distinction. The procedure goes one important step further than constraining the equation of state. It uses different combinations of simulated data of CMB, Weak Gravitational Lensing, and Supernovae. We explored the fact that the effect of dark energy on the expansion history must be consistent with the effect of dark energy on the growth factor of large-scale structure. The procedure is able to detect inconsistencies in this relation and thus provides a test to detect signatures of modified gravity models. [Preview Abstract] |
Sunday, April 23, 2006 10:54AM - 11:06AM |
I7.00003: Neutron background studies and results from the Cryogenic Dark Matter Search Raul Hennings-Yeomans Non-baryonic dark matter makes one quarter of the energy density of the Universe. The Weakly Interacting Massive Particle (WIMP) is a dark matter candidate with a scattering cross section with an atomic nucleus of the order of the weak interaction and a mass comparable to that of an atomic nucleus. Results of the two tower run from the Cryogenic Dark Matter Search (CDMS II), consisting of a total exposure of 34 kg-d for germanium and 12 kg-d for silicon, at the Soudan Underground Laboratory are presented. Also we present studies of the neutron background relevant for our upcoming 10-fold more sensitive 5-tower run, as well as for other experiments in search of dark matter. During the two-tower run, no nuclear-recoil events exceeding expected background were observed for a WIMP mass of 60 GeV/c$^{2}$. The limit from Ge (Si) is a factor of 2.5 (10) lower than previous results, allowing to set further constraints on the predictions of supersymetric models. Our further studies of the muon-induced neutron background based on Monte Carlo simulations show that by replacing part of the outer polyethylene of the CDMS II shield by a neutron multiplicity meter, for example by Gd-loaded liquid scintillator (0.5\% gadolinium content) with a PMT read out would allow us to better predict the absolute number of unvetoed nuclear recoils compared with present methods which rely on multiple nuclear recoil events. [Preview Abstract] |
Sunday, April 23, 2006 11:06AM - 11:18AM |
I7.00004: Precision Studies of Dark Energy with the LSST David Burke The proposed Large Synoptic Survey Telescope (LSST) will confront ``dark energy'' and ``dark matter'' with multiple precision probes of space and time, evolution of energy and matter, and the relation between cosmological kinematics and dynamics in a single deep survey of half the astronomical sky. The LSST optical throughput will be 100 times that of any existing facility. In the ten-year LSST mission the 2-D shapes and 3-D positions of over 3 billion galaxies will be measured (z $\le $ 3), and each year 250,000 Type Ia supernovae detected (z $\le $ 1). The LSST will enable studies of tomographic projections of shear correlations of weakly lensed galaxies, distributions of galaxies and clusters, and baryon acoustic oscillations. With LSST studies of supernova ``standard candles'' and ``synchronized clocks'' (time delays of multiply-lensed supernovae), these will precisely determine cosmological parameters. Six eigenmodes of the DE equation of state will be mapped by LSST data, and combined with CMB data, the lowest eigenvalues determined with percent-level accuracy. [Preview Abstract] |
Sunday, April 23, 2006 11:18AM - 11:30AM |
I7.00005: Long-wavelength perturbations as a test of dark energy Edmund Bertschinger Long-wavelength perturbations of a Robertson-Walker universe evolve like Robertson-Walker universes with perturbed spatial curvature or equation of state. This result, which is true in a much broader class of theories than general relativity, reduces the time-dependence of long-wavelength density perturbations to quadratures involving the Hubble expansion rate. Thus, measurements of the growth-rate of long-wavelength cosmological density perturbations, such as weak lensing or the abundance of galaxy clusters, should in principle provide no more information about dark energy than measurements of the expansion history made, e.g., by supernovae or baryon acoustic oscillations. Nevertheless, it is worthwhile to measure both the expansion history of the universe and the evolution of clustering because (1) the two methods have different systematic errors, (2) comparison of the two methods provides an independent test of the Cosmological Principle, and (3) comparison also provides information about long-wavelength entropy perturbations. A violation of the quadrature relation could signify the presence of new long-range forces. [Preview Abstract] |
Sunday, April 23, 2006 11:30AM - 11:42AM |
I7.00006: Dark matter detection with mini-CLEAN James Nikkel, M. Harrison, B. Jorns, W. Lippincott, D. McKinsey, A. Hime, D. Mei, K. Rielage, L. Stonehill, K. Coakley, M. Boulay, D. Gastler, E. Kearns mini-CLEAN is a planned WIMP detector containing approximately 100 kg of liquid neon or liquid argon scintillator viewed by 32 photomultipliers. The cryogens will be cooled with a pulse-tube refrigerator, allowing either liquid to be used as the active detection medium. The ability to exchange the two scintillators, with different sensitivities to WIMPs and fast neutrons, will allow both of these event populations to be distinguished and characterized. New measurements of the scintillation yield and time dependence for both gamma ray Compton scattering events and low energy nuclear recoil events in liquid neon and liquid argon show highly effective pulse-shape discrimination at low energies. Recent tests of photomultipliers at liquid neon temperature, as well as measurements of neon purification will be presented. The predicted sensitivity of mini-CLEAN to WIMP dark matter will be discussed. Results from mini-CLEAN will also provide key parameters for the design of a future 100-ton CLEAN detector, with simultaneous sensitivity to pp solar neutrinos and WIMPs. [Preview Abstract] |
Sunday, April 23, 2006 11:42AM - 11:54AM |
I7.00007: Neutron Background in WIMP Dark Matter Detectors Using Liquid Argon and Liquid Neon Andrew Hime, Dongming Mei 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. [Preview Abstract] |
Sunday, April 23, 2006 11:54AM - 12:06PM |
I7.00008: Updated RICE Bounds on Ultrahigh Energy Neutrino fluxes and interactions Shahid Hussain, Douglas McKay We explore limits on low scale gravity models set by results from the Radio Ice Cherenkov Experiment's (RICE) ongoing search for cosmic ray neutrinos in the cosmogenic, or GZK, energy range. The bound on, $M_{D}$, the fundamental scale of gravity, depends upon cosmogenic flux model, black hole formation and decay treatments, inclusion of graviton mediated elastic neutrino processes, and the number of large extra dimensions, d. We find bounds in the interval 0.9 TeV $<$ $M_{D}$ $<$ 10 TeV. Values d = 5, 6 and 7, for which laboratory and astrophysical bounds on LSG models are less restrictive, lead to essentially the same limits on $M_{D}$. [Preview Abstract] |
Sunday, April 23, 2006 12:06PM - 12:18PM |
I7.00009: The Search for Dark Matter Using the Gamma Ray Large Area Telescope (GLAST) Elliott Bloom, Ping Wang, Lawerence Wai The GLAST Large Area Telescope (LAT) Collaboration is one among several experimental groups, covering a wide range of approaches, pursuing the search for the nature of dark matter. However, as compared to direct and accelerator searches, the GLAST LAT has a unique ability to observe high energy gamma radiation emanating directly from WIMP annihilations in situ in the universe covering an important and complementary energy range with the ground-based TeV gamma-ray experiments. We describe the current status of feasibility studies for GLAST WIMP annihilation searches.. [Preview Abstract] |
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