Researchers on the Cryogenic Dark Matter Search, or CDMS, experiment are searching for WIMPs, which may make up dark matter.
Researchers built the CDMS detector to identify WIMPs through their interactions with nuclei in a section of the detector made of germanium crystals. When a nucleus is hit, it recoils, causing the whole germanium crystal to vibrate.
Theorists expect WIMPs to interact only once a year in each kilogram of space, and the energy caused by the nuclear recoil is very low. So the CDMS detector must distinguish between the effects of WIMP interactions and interactions by other particles such as electrons, photons or neutrons.
To minimize the amount of background noise, researchers placed the detector about a half-mile underground in the Soudan Mine in Minnesota, where rock can shield it from cosmic rays from space. Researchers know when an interaction comes from an electron or a photon because they can observe the amount of ionization the interaction causes. WIMPs would create very little. They also know when a neutron causes a distracting interaction because neutrons also interact with silicon detectors in the machine, something WIMPs are unlikely to do.