By Ron Cowen
Analyzing results of an experiment in a northern Minnesota mine, physicists report the possible detection of particles of dark matter — the proposed invisible material believed to account for about 80 percent of the mass of the universe. The physicists caution, however, that there’s about a one in four chance that ordinary subatomic particles, rather than dark matter, could account for the signals.
The experiment, called the Cryogenic Dark Matter Search, relies on 30 detectors made of germanium and silicon crystals cooled to just above absolute zero. The detectors record tiny vibrations imparted by a proposed type of dark matter called weakly interacting massive particles, or WIMPs. WIMPs streaming in from space would very rarely jostle the germanium nuclei, some 800 meters underground in the Soudan mine, generating a tiny amount of heat and slightly altering the charge on the detectors in a characteristic pattern.
In new analyses of data recorded in 2007 and 2008, researchers identified two events that might be attributed to WIMPs. Two members of the team, Jodi Cooley of Southern Methodist University in Dallas and Lauren Hsu of the Fermi National Accelerator Laboratory in Batavia, Ill., reported the findings December 17 during separate presentations. Cooley spoke at the SLAC National Accelerator Laboratory in Menlo Park, Calif., while Hsu spoke at Fermilab.