Dark matter is known to compose about 23% of the mass-energy density of the universe (ordinary matter makes up about 4%). While many possibilities for the origin and identity of dark matter particles have been proposed since the 1930s discovery of the first evidence for dark matter, so far there have been no confirmed identifications of dark matter with any known — or postulated — candidate.
Dark matter makes up more than half of the total mass of most galaxies, including our own Milky Way, and is known to be spread out well beyond the visible stars. This means it should be present in the solar system, and may be be detectable in laboratory experiments, as well as through the more traditional astrophysical observations.
The DMTPC experiment is being developed with the goal of detecting dark matter candidates via their interactions with ordinary matter in the laboratory. One type of dark matter candidate, known as a "Weakly Interacting Massive Particle,", or WIMP, may interact with nuclei of atoms. Such interactions, called nuclear recoils, could be observed by detecting the nuclear fragment emitted from the collision.
The prototype DMTPC detector under development is designed to detect these nuclear recoiis using a time-projection chamber filled with a low-density gas and instrumented with optical and charged readout. This prototype uses a directional detection method to reconstruct the direction of travel for low-momentum nuclear recoils — the so-called "head-tail" effect. The "smoking gun" signature would be a large number of nuclear recoils all pointing in the direction of the constellation Cygnus (the direction our solar system is moving as it orbits the galaxy).
The prototype is currently underground (to reduce background signals produced by cosmic rays) at the Waste Isolation Pilot Project near Carlsbad, New Mexico. Initial results are quite promising and we hope to build a full-scale dark matter detector based on these principles for use at an appropriate underground laboratory in the near future.