A wealth of observations, dating back 70 years, show that the universe is composed of >96% invisible matter and energy. The nature of these missing components is one of the most fundamental mysteries in physics, and has attracted broad attention from the public. The leading candidate for the invisible dark matter is a subatomic particle left over from the big bang known as the Weakly Interacting Massive Particle (WIMP). Such particles are also predicted by supersymmetry, a favored class of new particle models. If WIMPs exist, they are also the dominant mass in our own Milky Way. Though they only very rarely interact with conventional matter, they should nonetheless be detectable by sufficiently sensitive detectors on Earth, through their direct interaction with, and the ensuing recoil of, nuclei in a target material. The primary challenge in detecting them is reducing natural and cosmogenic radioactivity by up to 10 orders of magnitude.
A number of groups worldwide are searching for WIMP dark matter. CDMS II, has reported results from detectors of total mass 5 kg with a sensitivity of ~1 event/50 kg-days in Ge reached after 1 year net running. However, much larger detectors are needed to more completely test the WIMP hypothesis by improving sensitivity by over 3 orders of magnitude. A number of collaborations are investigating the use of noble liquids, such as Ar, Ne and Xe, for dark matter searches that promise to be readily scalable to multi-ton targets.
Text from LUX proposalUpdated 15 July, 2008