Cryogenic Dark Matter Search (CDMS):

This project looks for particles called WIMPs: Weakly-Interacting Massive Particles. These particles are similar to the neutrinos detected by MINOS, since WIMPs also easily pass through ordinary matter and are difficult to detect. Like neutrinos, WIMPs are also produced in collisions between other types of particles. The WIMPs that CDMS II searches for were not produced in an accelerator beam, but rather in particle collisions that took place during the hot conditions of the early universe, just moments after the Big Bang. It is possible that enough WIMPs were produced that they make up most of the matter in the universe today. In fact, there is very firm astronomical evidence from observations of stars and galaxies that most of the matter in the universe cannot be seen directly in telescopes. Instead, it must be observed indirectly through ts gravitational pull on the objects that we can see. This unknown stuff is called "dark matter." The WIMPs that CDMS II looks for could be this same stuff.

Detecting them is challenging because, in addition to their interactions being weak, the WIMPs are moving at only about one one-thousandth the speed of light, whereas the neutrinos produced at Fermilab are moving very close to the speed of light. Because of their relatively slow speed, the WIMPs are not visible in the scintillator material used by MINOS, but require more specialized devices that detect smaller amounts of energy. These devices are called "cryogenic" detectors. Cryogenic means they are very cold and must be operated in liquid-helium cooled refrigerators like the one installed in the nearby cavern. A CDMS detector is shown in the photo. It is inside its copper holder, with additional detectors and a wiring package in the background. Ultimately, CDMS II will consist of 7 stacks of 6 detectors each, made from germanium and silicon. Although the detector is relatively small in size compared to MINOS, CDMS II is a complex experiment that requires the expertise of many different research groups that work together in a scientific collaboration. Groups from all over the country come to Soudan to take advantage of the unique conditions available in the mine. The groups working on CDMS II, a $15 million project, come from the following institutions: Brown University, Case Western Reserve University, Fermilab, Lawrence Berkeley National Laboratory, the National Institute of Standards and Technology, Princeton University, Santa Clara University, Stanford University, the University of California at Berkeley and at Santa Barbara, the University of Colorado at Denver, and the University of Minnesota.