Underground experiment may have found dark matter

An underground experiment deep in the Soudan mine in Minnesota, US, may have detected a type of dark-matter particle.

According to a report in Nature News, the huge Cryogenic Dark Matter Search (CDMSII) experiment contains a rack of supercooled hockey-puck-sized silicon and germanium detectors nestled within Russian-doll layers of shielding.

Two weeks ago, the CDMSII collaboration published a paper showing that two particles had penetrated its detector's defences - particles that, given the lack of any other particle activity down in the frigid quiet of the detectors, looked very much like dark matter.

Dark matter is thought to make up 85% of the mass in the Universe, but has not been detected directly - quite.

The attention-grabbing claim of the CDMSII collaboration has many physicists thinking - but not yet convinced - that the team could be on to something.

Just a stone's throw from the CDMSII experiment, across the subterranean cavern, lies a far smaller box that is thickening the dark-matter plot.

The box contains a single germanium hockey puck, similar to those in the CDMSII experiment but operated by the Coherent Germanium Neutrino Technology (CoGeNT) collaboration and tuned to detect incoming particles with much lower masses than the CDMSII.

It began collecting data in December 2009, and, after just 56 days, the group is reporting hundreds of particle strikes that cannot be explained other than by invoking dark matter.

"If it's real, we're looking at a very beautiful dark-matter signal," said Juan Collar, a physicist at the University of Chicago and CoGeNT spokesperson.

Confirmation of the result would radically shift attention to experiments that are sensitive to lower energies.

The CoGeNT experiment looks for a type of dark-matter particle called a WIMP, or Weakly Interacting Massive Particle.

The new data point to a WIMP with a mass in the range of 7-11 billion electronvolts.

Theorists have conjured up hundreds of mathematically consistent models for producing WIMPs of different masses in the early Universe, and the particles detected by CoGeNT fit well in the realm of the theoretically possible.