An experiment in Minnesota is the first to bolster a long-contested claim that detectors a continent away have found evidence of particles called WIMPs.
WIMPs are theorized particles considered to be leading candidates for dark matter, invisible material believed to make up more than 80 percent of the matter in the universe. In the Minnesota experiment, called COGENT, a hockey puck–sized chunk of germanium deep in a former iron mine attempts to record rare collisions with WIMPS.
In 15 months’ worth of data, COGENT researchers detected a seasonal variation in the collision rate — higher in summer and lower in winter — similar to that seen for 13 years by a larger experiment, using different detectors, in Italy. Researchers with that experiment, DAMA/LIBRA, have attributed the results to the Earth’s motion through a cloud of WIMPs (for weakly interacting massive particles) (SN: 5/10/08, p. 12). But many physicists have doubted that interpretation because, until now, no other experiment had found similar results.