On Saturday April 13, Kevin McCarthy, from the MIT group on behalf of the SuperCDMS Collaboration, has presented the blind analysis results of the largest exposure with silicon detectors during CDMS-II operation. The collaboration has previously published the results of the entire germanium detector exposure [Science 327, 1619 (2010)] which resulted in 2 events in the signal region and an estimated background of 0.9 events. Afterward, our likelihood analysis concluded that these were more likely leakage surface electrons rather than nuclear recoils.

Increased interest in the low mass WIMP region motivated us to complete the analysis of the silicon detector exposure which is less sensitive than germanium for WIMP masses above 15 GeV/c², but more sensitive for lower masses. The analysis resulted in 3 events and the estimated background is 0.7 events.

Monte Carlo simulations have shown that the probability that a statistical fluctuation of our known backgrounds could produce three or more events anywhere in our signal region is 5.4%. However, they would rarely produce a similar energy distribution. A likelihood analysis that includes the measured recoil energies of the three events gives a 0.19% probability for a model including only known background when tested against a model that also includes a WIMP contribution. This ~3-sigma confidence level does not rise to the status of a discovery, but does call for further investigation.

If the result is interpreted as spin-independent scattering of WIMPs, a mass around 8.6 GeV/c² and a WIMP-nucleon cross section of 1.9E-41 cm² are favored. For the simplest theories of WIMP interactions and using the standard dark matter halo model, the allowed region is in tension with exclusion limits from the XENON collaboration. A paper has been submitted to the arXiv and to PRL.

We will probe this WIMP sector with our operating germanium detectors in the SuperCDMS Soudan experiment, and we are considering using silicon detectors in future experiments.

CDMS-II was funded by DOE and NSF in the US and by NSERC in Canada.

Dark Matter Search Results Using the Silicon Detectors of CDMS II. arXiv astro-ph.CO, (2013), arXiv:1304.4279 Silicon Detector Results from the First Five-Tower Run of CDMS II. arXiv astro-ph.CO, (2013), arXiv:1304.3706 E. Figueroa-Feliciano's presentation at Light Dark Matter 2013. K. McCarthy's presentation at APS. B. Cabrera's Panofsky Prize presentation at APS. B. Sadoulet's Panofsky Prize presentation at APS. Fermilab Today and SLAC Today features. Symmetry Magazine feature. Upper Limits and Contour Curves from CDMS II Si http://lanl.arxiv.org/abs/1304.4279

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)

Click here for the slides used in the Jodi Cooley presentation(pdf)

High resolution .mov copies of the Jodi Cooley presentation:
(822 MB Quicktime)
(403 MB MPEG-4)

Other talks:
Lauren Hsu Fermilab (pdf) & Video of the Lauren Hsu presentation
Talk of B. Sadoulet at the APC (Paris) 11 February 2010 (pdf)
Talk of J. Hall at the Marina del Rey Dark Matter workshop 26 February 2010 (pdf)
Talk of P. Brink at the Marina del Rey Dark Matter workshop 26 February 2010 (pdf)

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.... Read more at APS Physics