The evidence for nonbaryonic dark matter is compelling. An impressive variety of observational data has convinced cosmologists that protons and neutrons, and indeed all of the particles known from the laboratory, account for less than 20% of the mass of matter in the cosmos. Cosmologists and particle theorists favor the hypothesis that the predominant dark-matter particles are WIMPs (weakly interacting massive particles) with a mass on the order of 100 GeV (a hundred times the proton mass) and a scattering cross section typical of the weak nuclear interactions.
The existence of WIMPs is predicted by supersymmetry theory, theories with extra spacetime dimensions, and other attempts to speculate beyond particle theory's standard model. WIMP searches are proceeding on two fronts: The Large Hadron Collider at CERN will soon be providing 14-TeV proton–proton collisions. If WIMPs are not much heavier than 200 GeV, the hope is that they will be found among...
