Additional information related to the CDMS experiment
What is dark matter?
Most of the ordinary matter is invisible, too. It exists across the universe in form of hydrogen, dust clouds and very dim clumps of matter called massive compact halo objects. These MACHOs include planets and cold dead stars like brown dwarfs and black holes.
Neutrinos, very light particles left over from the big bang in massive quantities, make up a small amount of the dark matter that is not made of quarks. WIMPs, or weakly interactive massive particles, may make up the rest. Neutrinos move at nearly the speed of light. That’s why they are considered "hot dark matter."
What is a WIMP?
What is supersymmetry?
The lightest neutral supersymmetric particle is the neutralino. With an expected mass of 50-1,000 billion electron volts (GeV) – the mass of a proton is 1 GeV — and weak interaction with everyday matter, the neutralino is a prime candidate for being a WIMP.
If it is a WIMP, it travels through the universe at 1/1000 the speed of light, making it "cold dark matter." Neutralinos were produced at the beginning of the universe but exist in fewer numbers than the neutrino because their great mass makes them harder to produce, and they annihilate each other. Both types of particles pass through the Earth in large quantities.
How does the CDMS experiment work?
When a WIMP hits a germanium nucleus, the nucleus recoils and vibrates the whole germanium crystal. This warms the thin aluminum and tungsten outer layers, which an electrical circuit measures. Photons and electrons, however, strike the germanium's electrons. A charge collection plate measures ionization resulting from this type of collision and uses it to separate these interactions from those of WIMPs. The ratio of charge to heat for each event tells whether a particle struck the nucleus, as WIMPs do, or simply rattled the electrons surrounding the nucleus, as most background particles do.
Incoming neutrons also strike the germanium nucleus, so they more closely resemble WIMPs. The germanium detectors sit in a stack with detectors made of silicon. A silicon atom has a smaller nucleus, and so will be hit less frequently by WIMPs. The strong nuclear force does not affect WIMPs, but it does affect neutrons and so neutrons will hit nuclei of different sizes at about the same rate. A higher collision rate in the germanium than the silicon will indicate the interaction of WIMPs.
Why is the CDMS experiment underground?
Why are the CDMS detectors so cold?
|last modified 02/22/2008 email Fermilab|