Sunday, April 28, 2013

Cryogenic dark matter detection, redux

About 3.5 years ago, I posted about the technology used by the CDMS collaboration to look for dark matter using clever solid-state detectors.  These folks have some news that is, as is often the case in any novel particle detection experiment, intriguing but not yet definitive.  This paper is probably the best place to see a summary of the results.  In their CDMS II run, the team had 19 germanium-based and 11 silicon-based detectors (cooled to 0.04 K!) running for five years (2003-2008) in an old mine in Minnesota (to cut down on cosmic ray background).  This paper reports results from the Si detectors, where after a lengthy blind analysis they see three events that look interesting.  Since germanium has a higher atomic number than Si, the idea of running the two materials in parallel was to have a cross-check and provide some information about how the searched-for weakly interacting massive particles (WIMPs) might interact with ordinary matter as a function of energy.  I should also note that the collaboration is now running "SuperCDMS" with a larger mass of germanium (9 kg) since 2011, and will eventually expand up to 200 kg of Ge running in Soudan in Ontario.  It's interesting that their earlier analysis from their Ge detectors reported no candidate events (as far as I can tell), while the analysis of the Si detectors shows three candidate events.  My understanding is that this could have to do with the mass range of the WIMPs, but I would be happy if someone would provide more context in the comments below.  Either way, I think it's great to see how condensed matter physics (and in particular cool device fabrication, as in the superconducting transition-edge sensors used here) can have an impact on Big Questions like dark matter.

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