EDELWEISS
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Principle
Any direct detection experiment of WIMPs is faced with two main difficulties. First, the nuclear recoil energy induced by a WIMP interaction is very small, of the order of a few keV to a few tens of keV, depending on the respective neutralino and nucleus masses. The energy threshold of the detector has to be very low. The EDELWEISS collaboration uses cryogenic detectors at very low temperatures (about 20 mK), each made of a massive (320 g) monocrystal of high purity germanium. The recoil energy of a Ge nucleus is converted into heat (measured by a temperature rise whith a precision better than one millionth of a degree) and also into ionisation (ionisation signals of a few hundred electrons are detectable). The energy threshold is thus as low as 10 keV.
