About the CDMS II Experiment The CDMSII experiment preceded the SuperCDMS experiment. It aimed to measure the recoil energy imparted to detector nuclei through neutralino-nucleon collisions by employing sensitive phonon detection equipment coupled to arrays of cryogenic germanium and silicon crystals. The detectors themselves, known as ZIP detectors, featured state-of-the-art thin film superconducting technology. Each 250g germanium or 100g silicon crystal provided two sets of information about interactions with incident particles. Thus allowing the search for weakly-interacting massive particles, or WIMPS, whose discovery could resolve the dark matter problem, revolutionizing particle physics and cosmology. The CDMSII experiment is located deep underground in the Soudan mine in Minnesota, USA. This location provides vastly improved shielding from cosmogenic events which will reduce interference of known backgrounds particles. The CDMSII experiment program seeked to combine high fiducial detector mass and extensive run time with reduced backgrounds to advance WIMP dark matter knowledge significantly.

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Scaling up the search for dark matter

Karl van Bibber; Published January 5, 2009: New upper limits on the spin-independent interaction of WIMPs and nucleons marks the latest volley in the worldwide effort to detect and identify particle dark matter.
The dynamical evidence for dark matter in the universe of anomalously large velocities of stars within galaxies, and galaxies within clusters —goes back three-quarters of a century [1]. Within the past decade, precision measurements of cosmological parameters have pinned down the partitioning of the energy density of the universe rather neatly: dark energy accounts for roughly three-fourths, and matter of all forms makes up only a quarter. Of the latter, nonbaryonic dark matter accounts for about five parts in six [2]. What this elusive invisible matter actually is represents one of the pre-eminent questions in all of science. In Physical Review Letters, Ahmed et al. [3] report results from one of the collaborations involved in the hunt for dark matter that place new upper bounds on the extent of any possible interaction between certain kinds of dark-matter particles and normal matter.

One or more species of particle relics from the big bang are increasingly favored as the elusive dark-matter, with well-motivated beyond-Standard-Model candidates such as axions [4] and weakly interacting massive particles (WIMPs) [5] at the top of a short list—although one must be open to surprise. At present the neutralino, or WIMP, from the so-called supersymmetric theories enjoys wide currency as the favorite contender. These theories have the attractive feature of both preventing particle masses from being much heavier than they are, as well as unifying three of the four forces of nature. Such particles are expected to be in the range of 10 to 1000 times the proton mass, and should interact with cross sections characteristic of the weak interaction scale.... Click here to continue reading at APS Physics
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Low-threshold results

Results from a Low-Energy Analysis of the CDMS II Germanium Data, Phys. Rev. Lett. 106 131302 (2011)
We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below ~10 GeV/c^2. This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c^2 and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments. Papers: arXiv:1011.2482 and PRL paper

Low-threshold analysis of CDMS shallow-site data, published in Phys. Rev. D82, 122004 (2010)
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 ~224 g germanium and two ~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 ~1 keV and ~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^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 GeV/c^2 and 4 GeV/c^2. Papers: arXiv:1010.4290v3 and PRD paper

Latest results of CDMS-II, December 17, 2009

Summary of the results (pdf) Science article 2/12/2010
Astrophysical observations indicate that dark matter constitutes most of the mass in our universe, but its nature remains unknown. Over the past decade, the Cryogenic Dark Matter Search (CDMS II) experiment has provided world-leading sensitivity for the direct detection of weakly interacting massive particle (WIMP) dark matter. The final exposure of our low-temperature germanium particle detectors at the Soudan Underground Laboratory yielded two candidate events, with an expected background of 0.9 ± 0.2 events. This is not statistically significant evidence for a WIMP signal. The combined CDMS II data place the strongest constraints on the WIMP-nucleon spin-independent scattering cross section for a wide range of WIMP masses and exclude new parameter space in inelastic dark matter models. (Abstract) Click for: Printed report (pdf) and Supplementary Online Material (pdf)

Announcement talks December 12, 2009 Click here for more publications!

This work is supported by the National Science Foundation and the Department of Energy