WIMP
This article is about the hypothetical class of particles. In human-computer interaction, WIMP stands for the "window, icon, menu, pointer" paradigm. A wimp is also a person who lacks confidence, is irresolute and wishy-washy.
In astrophysics, WIMPs, or weakly interacting massive particles, figure into one explanation of the dark matter problem. The particles are called "weakly interacting" because they seem not to have much interaction with normal matter (electrons, protons, and neutrons) other than gravitational attraction (thus "massive").
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Theoretical Arguments
The existence of WIMPs in nature is hypothetical at this point. However, in various astrophysical and cosmological problems related to dark matter they are considered as very likely to exist. The main theoretical characteristics of a WIMP particle are:
A large population of particles with these properties in the universe could explain a number of astronomical measurements that call for more mass inside a part of space than there is deduced by accounting for all visible matter, and where the effect of the gravitational interaction rearranges the heavy particles only slowly. The latter destinguishes a WIMP from a standard light particle like the neutrino. This is important, since scientists seem to need two types of hypothetical dark matter: "Cold" and "Hot", which stands for "slow" and "fast" moving. WIMPs are considered one of the main candidate for "Cold Dark Matter", the other being MACHOs. (These names were chosen to be in stark contrast, intentionally.) Also, in contrast to MACHOs, WIMPs can most likely not be integrated into the currently known structure of particle physics. Their discovery could therefore have wide-ranging consequences in other sciences besides astrophysics.
Due to their neccessary weak interaction with matter, this could turn out to be difficult. Just like neutrinos, they could pass through matter like the Sun or the Earth without any effects. It is therefore only hoped that a large number of WIMPs crossing a large "detection volume" would create some kind of reaction at least a few times a year. The general strategy of current attempts to detect WIMPs is to find very sensitive systems, that then can be scaled up to large volumes. This follows the lessons learned from the history of the discovery and (by now) routine detection of the neutrino.
A technique used by the Cryogenic Dark Matter Search (CDMS) detector at the Soudan Mine relies on multiple very cold silicon and germanium crystals. The crystals (each about the size of a beer can) are cooled down to about 70 millikelvins. A layer of metal (aluminum and tungsten) at the surfaces is used to detect a WIMP passing through the crystal. This design hopes to detect vibrations in the crystal matrix generated by an atom being "kicked" by a WIMP. The tungsten metal detectors are held at the critical temperature so they are in the superconducting state. Large cyrstal vibrations will generate heat in the metal and is detectable because of a change in resistance.
Another way of detecting atoms "knocked about" by a WIMP is to use scintillating material, so that light pulses are generated by the moving atom. An example for this technique is the DAMA detector in Italy. It uses multiple materials to easier identify false signals from other light creating processes. This experiment currently sees an annual change in the rate of signals in the detector. But scientists are still discussing, if this represents a positive detection or some unexplained effect in the detector system itself. This dispute arises from the fact that other experiments, e.g. EDELWEISS, have contradictory results that seem to exclude interpretation of the DAMA data as stemming from WIMPs.Experimental Detection
There are multiple measurements that provide indirect evidence for the existence of "Cold Dark Matter", however the existence of WIMPs can only be proven by direct measurement of these particles.