Background
Observations of the large-scale structure of the universe show that matter is aggregated into very large structures that would not have time to have formed under the force of their own self-gravitation. It is generally believed that some form of missing mass is responsible for increasing the gravitational force at these scales, although this mass has not been directly observed. This is a problem; normal matter in space will heat up until it gives off light, so if this missing mass exists, it is generally assumed to be in a form that is not commonly observed on earth.
A number of proposed candidates for the missing mass have been put forward over time. Early candidates included heavy baryons that would have had to be created in the big bang, but more recent work on nucleosynthesis seems to have ruled most of these out. Another candidate are new types of particles known as weakly interacting massive particles, or "WIMP"s. As the name implies, WIMPs interact weakly with normal matter, which explains why they are not easily visible.
Detecting WIMPs thus presents a problem; if the WIMPs are very weakly interacting, detecting them will be extremely difficult. Detectors like CDMS and similar experiments measure huge numbers of interactions within their detector volume in order to find the extremely rare WIMP events.
Read more about this topic: Cryogenic Dark Matter Search
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