M. J. Attisha

Limits on Spin-Independent Interactions of Weakly Interacting Massive Particles with Nucleons from the Two-Tower Run of the Cryogenic Dark Matter Search

We report new results from the Cryogenic Dark Matter Search (CDMS II) at the Soudan Underground Laboratory. Two towers, each consisting of six detectors, were operated for 74.5 live days, giving spectrum-weighted exposures of 34 kg-d for germanium and 12 kg-d for silicon targets after cuts, averaged over recoil energies 10-100 keV for a WIMP mass of 60 GeV. A blind analysis was conducted, incorporating improved techniques for rejecting surface events. No WIMP signal exceeding expected backgrounds was observed. When combined with our previous results from Soudan, the 90% C.L. upper limit on the spin-independent WIMP-nucleon cross section is 1.6 x 10^{-43} cm^2 from Ge, and 3 x 10^{-42} cm^2 from Si, for a WIMP mass of 60 GeV. The combined limit from Ge (Si) is a factor of 2.5 (10) lower than our previous results, and constrains predictions of supersymmetric models.

First Results from the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search (CDMS) experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg-d of Ge net exposure after cuts for recoil energies between 10--100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the worlds lowest exclusion limits on the coherent WIMP-nucleon scalar cross-section for all WIMP masses above 15 GeV, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10^{-43} cm^2 at a WIMP mass of 60 GeV.

Low-threshold analysis of CDMS shallow-site data

Data taken during the final shallow-site run of the first tower of the Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with improved sensitivity to small energy depositions. Four {approx}224 g germanium and two {approx}105 g silicon detectors were operated at the Stanford Underground Facility (SUF) between December 2001 and June 2002, yielding 118 live days of raw exposure. Three of the germanium and both silicon detectors were analyzed with a new low-threshold technique, making it possible to lower the germanium and silicon analysis thresholds down to the actual trigger thresholds of {approx}1 and {approx}2 keV, respectively. Limits on the spin-independent cross section for weakly interacting massive particles (WIMPs) to elastically scatter from nuclei based on these data exclude interesting parameter space for WIMPs with masses below 9 GeV/c{sup 2}. Under standard halo assumptions, these data partially exclude parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT experiments data as WIMP signals, and exclude new parameter space for WIMP masses between 3 and 4 GeV/c{sup 2}.

Exclusion limits on the WIMP-nucleon cross section from the first run of the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si detectors to seek Weakly Interacting Massive Particles (WIMPs) via their elastic scattering interactions with nuclei. Simultaneous measurements of both ionization and phonon energy provide discrimination against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with>99.99% efficiency. Electromagnetic events very near the detector surface can mimic nuclear recoils because of reduced charge collection, but these surface events are rejected with>96% efficiency by using additional information from the phonon pulse shape. Efficient use of active and passive shielding, combined with the the 2090 m.w.e. overburden at the experimental site in the Soudan mine, makes the background from neutrons negligible for this first exposure. All cuts are determined in a blind manner from in situ calibrations with external radioactive sources without any prior knowledge of the event distribution in the signal region. Resulting efficiencies are known to ~10%. A single event with a recoil of 64 keV passes all of the cuts and is consistent with the expected misidentification rate of surface-electron recoils. Under the assumptions for a standard dark matter halo, these data exclude previously unexplored parameter space for both spin-independent and spin-dependent WIMP-nucleon elastic scattering. The resulting limit on the spin-independent WIMP-nucleon elastic-scattering cross-section has a minimum of 4x10^-43 cm^2 at a WIMP mass of 60 GeV/c^2. The minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering cross-section is 2x10^-37 cm^2 at a WIMP mass of 50 GeV/c^2.

Limits on spin-dependent WIMP-nucleon interactions from the Cryogenic Dark Matter Search

The Cryogenic Dark Matter Search (CDMS) is an experiment to detect weakly interacting massive particles (WIMPs) based on their interactions with Ge and Si nuclei. We report the results of an analysis of data from the first two runs of CDMS at the Soudan Underground Laboratory in terms of spin-dependent WIMP-nucleon interactions on 73Ge and 29Si. These data exclude new regions of spin-dependent WIMP-nucleon interaction parameter space, including regions relevant to spin-dependent interpretations of the annual modulation signal reported by the DAMA/NaI experiment.

The SuperCDMS Experiment

Modest improvements in the level and/or discrimination of backgrounds are needed to keep backgrounds negligible during the three phases of SuperCDMS. By developing production designs that require only modest testing, detector production rates may be improved sufficiently to allow an exposure of 500 ton d within a reasonable time and budget. Overall, the improvement estimates described above are conservative. Previous development efforts have shown that some areas prove easier and provide larger factors while others prove more difficult. The conservative estimates together with the broad approach reduce the risk and give us confidence that we will succeed, providing the surest way to probe to WIMP-nucleon cross sections of 10{sup -46} cm{sup 2}.

CDMS, Supersymmetry and Extra Dimensions

The CDMS experiment aims to directly detect massive, cold dark matter particles originating from the Milky Way halo. Charge and lattice excitations are detected after a particle scatters in a Ge or Si crystal kept at ∼30 mK, allowing to separate nuclear recoils from the dominating electromagnetic background. The operation of 12 detectors in the Soudan mine for 75 live days in 2004 delivered no evidence for a signal, yielding stringent limits on dark matter candidates from supersymmetry and universal extra dimensions. Thirty Ge and Si detectors are presently installed in the Soudan cryostat, and operating at base temperature. The run scheduled to start in 2006 is expected to yield a one order of magnitude increase in dark matter sensitivity.

First CDMS II WIMP Search Results from the Soudan Underground Laboratory

D.S. Akerib, M.S. Armel-Funkhouser, M.J. Attisha, L. Baudis, D.A. Bauer, P.L. Brink, R. Bunker, B. Cabrera, D.O. Caldwell, C.L. Chang, M.B. Crisler, P. Cushman, R. Dixon, M.R. Dragowsky, D.D. Driscoll, L. Duong, R. Ferril, J. Filippini, R.J. Gaitskell, D. Holmgren, M.E. Huber, S. Kamat, A. Lu, R. Mahapatra, V. Mandic, P. Meunier, N. Mirabolfathi, H. Nelson, R. Nelson, R.W. Ogburn, T.A. Perera, E. Ramberg, W. Rau, A. Reisetter, R.R. Ross, T. Saab, B. Sadoulet, J. Sander, C. Savage, R.W. Schnee, D.N. Seitz, B. Serfass, A.J. Sirois, K.M. Sundqvist, J-P.F. Thompson, G. Wang, S. Yellin, and B.A. Young

Latest Results From The CDMS-II Cold Dark Matter Search

The CDMS‐II collaboration’s Cold Dark Matter search presently sets the most competitive exclusion limit in the world for the direct detection of the hypothesized Weakly Interacting Massive Particles (WIMPs) that constitute the cold dark matter of the Universe. Our experiment utilizes Ge (and Si) crystals as the target detectors, each with a mass of 250 g (100 g) and cooled to 30 mK. To eliminate natural radioactive sources as background the experiment is conducted in a well‐shielded environment in the Soudan Mine, Minnesota, and has been operating for the last two years. To aid in the identification of a possible WIMP‐candidate event, the detectors are designed to measure both the ionization and athermal phonon signals produced by each candidate event. The athermal phonon signal is measured using superconducting aluminum films on the crystal surface connected to tungsten transition edge sensors. The latest WIMP‐search results from Soudan will be presented, along with projections for the future.