The Cryogenic Dark Matter Search at UC Berkeley
The CDMS Experiment
The Cryogenic Dark Matter Search (CDMS) is an experiment to directly detect the interactions of dark matter particles in terrestrial detectors. The second Version of this experiment, CDMS II, collected data from 2006 to 2008 on 30 germanium and silicon detectors in a low-radioactivity facility at the Soudan Underground Laboratory in northern Minnesota. While data is no longer being collected on the CDMS II detectors the results are still being analyzed. So far, the CDMS II experiment has set the most stringent limits on Wimp detection. CDMS is a collaboration of a dozen institutions around the world.
CDMS seeks to detect Weakly Interacting Massive Particles (WIMPs), heavy neutrino-like particles that are the leading candidate for the universe's dark matter. Using sensitive detectors, we hope to discern the impacts of astrophysical WIMPs in terrestrial detectors. These efforts are strongly complementary to investigations of dark matter at particle colliders and indirect searches with advanced telescopes.
For more information on the evidence for dark matter and methods for its detection, see the CDMS education page.
CDMS uses advanced semiconductor detectors to distinguish nuclear recoils (due to WIMPs or neutrons) from electron recoils (due to most radioactive backgrounds) at keV energies. The current experiment uses Z-sensitive Ionization and Phonon (ZIP) detectors to measure both the ionization and phonon signals from each particle impact. The ratio of these signals distinguishes electron and nuclear recoils with great accuracy, while timing information from the phonon signals can be used to reconstruct event position (including depth within the detector).
ZIP detectors are fabricated at Stanford and their performance characterized at Berkeley and other institutions. Berkeley is also deeply involved with prototypes of future detector designs and with investigations of detector physics processes.
For more information on the zip detectors used in the CDMSII experiment check out the ZIP page.
Soudan Underground Laboratory
WIMPs are expected to interact very weakly with ordinary matter, penetrating deeply into the earth with ease. To shield against cosmic rays and the neutrons they produce, the main CDMS installation is located in a low-radioactivity installation 1/2-mile underground in Soudan Underground Laboratory. Soudan, an abandoned iron mine in northern Minnesota, is also the home of the far detector for the MINOS neutrino oscillation experiment.
CDMS has yet to detect any dark matter, but it has set the world's most stringent limits on its interactions with ordinary matter. Our most recent run of 100 live days at Soudan saw zero events, leading to the world-leading upper limits shown at right. Further runs at Soudan are underway to improve our sensitivity yet further.