KIP - Cryogenic particle detection - Dark matter


Dark Matter Search

Several astronomical observations, like the velocity of rotation of spiral galaxies (Fig. 1), indicate that the luminous mass represents only 10 to 30% of the total mass, which determines the dynamics. The origin and consistency of the missing mass, which is called dark matter, is unknown. There are many different theoretical approaches to explain what dark matter consists of. Recent observations suggest that dark matter is not made of a single component, but is a combination of different types of matter. One component, might be weakly interacting massive particles (WIMPs), which play an important rule in certain extension of the standard model of elementary particles. In a simplified picture these particles can be viewed as very massive neutrinos, which are gravitationally bound to galaxies in form of a spherical helo and have a thermal distribution of velocity.

Several cryogenic detectors are currently under construction (some partially already operating) to detect WIMPs. The expected very small cross-section makes the detections of WIMPs extremely difficult. A concept, which is often used, is the determination of the nuclear recoil after the elastic scattering of a WIMP with a nucleus in a solid. In general such a nuclear recoil produces athermal excitations in the absorber. These excitations propagate through the solid a thermalize mainly at the surface, where the thermometer is attached. One very important point in connection with WIMP search experiments is the reduction of background events, because the expected event rate for WIMPs is very low. Therefore such experiments have to be performed in special underground laboratories. The reduce the influence of the natural radioactivity massive screening and special coincidence systems are used. An important signature for identification of WIMP events should be a seasonal variation of the signal because the relative motion of earth and milky way.
 
CRESST-Collaboration

CDMS-Collaboration

ROSEBUD, University of Zaragoza, Spain

CUORE, Milano, Italy

MACHe3, CNRS Grenoble, France

EDELWEISS-Collaboration

ORPHEUS, University of Bern, (Switzerland)

Fig. 1: Measured rotation speed of a spiral galaxy (red) in comparison with the expected curve if only the luminous mass is considered (black).
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