Astronomy Colloquium

Astrophysical observations indicate that at least 90% of the mass of any galaxy -- and as much as 98% of the mass of the universe -- is in the form of matter that cannot be seen. Furthermore, most of this matter isn't even made from protons and neutrons -- or any other known particles. What could this matter be and how can we find out? Perhaps the best motivated possibility is weakly interacting massive particles (WIMPs) left over from the Big Bang; these particles naturally arise, for example, under supersymmetry. Detection of these particles requires exquisite
rejection of interactions from natural radioactivity, as achieved using the CDMS experiment's cryogenically cooled crystals of silicon or germanium with thin-film sensors to detect both ionization and athermal phonons. Operation of these novel detectors and the prospects for discovering what's the matter in the universe will be discussed.