EDELWEISS (Expérience pour DEtecter Les WIMPs En Site Souterrain) is a dark matter search experiment located at the Modane Underground Laboratory in France. The experiment uses cryogenic detectors, measuring both the phonon and ionization signals produced by particle interactions in germanium crystals. This technique allows nuclear recoils events to be distinguished from electron recoil events.
The EURECA project is a proposed future dark matter experiment, which will involve researchers from EDELWEISS and the CRESST dark matter search.
Experience to Detect WIMPs in Underground Site
WIMPS Weakly Interacting
Massive Particles
EDELWEISS is located in the Modane underground laboratory, in the Fréjus road tunnel between France and Italy, below 1800m of rock. A 20 cm lead shield reduces the gamma background, and a polyethylene shield reduces the neutron flux. All materials close to the detectors are screened for radiopurity. A dilution refrigerator is used to cool the detectors, built in the opposite orientation to most instruments with the detectors at the top and the refrigeration mechanism below.
EDELWEISS uses high purity germanium cryogenic bolometers cooled to 20 milliKelvin above absolute zero. The phonon and ionization signals produced by a particle interaction are measured. This allows background events to be rejected as nuclear recoils events (produced by WIMP or neutron interactions) produce much less ionization than electron recoil events (produced by alpha, beta and gamma radiation). The detectors are similar to those used by the CDMS experiment. Simultaneous detection of ionization and heat with semiconductors at low temperature was an original idea by Lawrence M. Krauss, Mark Srednicki and Frank Wilczek.[1]
A major limitation of early detectors was the problem of surface events. Due to incomplete charge collection, a particle interaction near the surface of the crystal gave no ionization signal, so electron recoils near the surface could be mistaken for nuclear recoils. To avoid this, the collaboration developed new detectors with interdigitised electrodes. Different voltages are applied to a series of electrodes so the direction of electric field is different near the surface of the crystal, allowing over 99.5% of surface events to be rejected…
https://en.wikipedia.org/wiki/EDELWEISS