Astroparticle Physics

13.2 Motivation for Dark Matter 277detector without significant interaction. Primordially producedsupersymmetric particles would have decayed alreadya long time ago, apart from the lightest supersymmetric particles,which are expected to be stable if R parity is conserved.These would lose a certain amount of energy in collisionswith normal matter, that could be used for their detection.Unfortunately, the recoil energy transferred to a targetnucleus in a WIMP interaction (mass 10–100 GeV) is rathersmall, namely in the range of about 10 keV. Still one tries tomeasure the ionization or scintillation produced by the recoilingnucleus. Also a direct calorimetric measurement ofthe energy deposited in a bolometer is conceivable. Becauseof the low energy Q to be measured and the related minutetemperature riseT = Q/c sp m (13.22)(c sp is the specific heat and m the mass of the calorimeter),these measurements can only be performed in ultrapurecrystals (e.g., in sapphire) at extremely low temperatures(milli-Kelvin range, c sp ∼ T 3 ). It has also been consideredto use superconducting strips for the detection, which wouldchange to a normal-conducting state upon energy absorption,thereby producing a usable signal.Based on general assumptions on the number density ofWIMPs one would expect a counting rate of at most oneevent per kilogram target per day. The main problem in theseexperiments is the background due to natural radioactivityand cosmic rays.Due to their high anticipated mass WIMPs could also begravitationally trapped by the Sun or the Earth. They wouldoccasionally interact with the material of the Sun or Earth,lose thereby energy, and eventually obtain a velocity belowthe escape velocity of the Sun or the Earth, respectively.Since WIMPs and in the same way their antiparticles wouldbe trapped, they could annihilate with each other and provideproton–antiproton or neutrino pairs. One would expectto obtain an equilibrium between trapping and annihilationrate.The WIMP annihilation signal could be recorded in largeexisting neutrino detectors originally designed for neutrinoastronomy. Also large neutrino detectors under construction(ANTARES 6 or IceCube) would have a chance to pick up aWIMP signal.6 ANTARES – Astronomy with a Neutrino Telescope and Abyssenvironmental RESearchrecoil energyionization and scintillationof recoiling nucleuscalorimetric measurementbolometerexpected WIMP rategravitational bindingto the solar systemWIMP annihilationpossible recordingin neutrino detectors