EXPERIMENTS SEARCHING FOR NONBARYONIC DARK-MATTER

It is increasingly likely that the universe has critical density, the only time-stable value, and that therefore at least 90% of its mass is in a nonbaryonic form outside the Standard Model of particle physics. Probably similar to 70% of this mass is cold dark matter and the rest hot, in the form of neutrinos with total mass summed over all active species of similar to 5 eV. If the solar nu(e) and atmospheric nu(mu) deficits also require neutrino mass, then there are only two viable patterns for those masses: (1) the nu(e), nu(mu), and nu(tau), are all similar to 2 eV, or (2) the nu(e), and a sterile neutrino, nu(1), can be light, and the nu(mu), and nu(tau), are similar to 3 eV. Terrestrial experiments are needed to determine the neutrino masses, and there are already hints of effects from the LSND neutrino oscillation experiment and possibly from neutrinoless double beta decay. Information on cold dark matter can be obtained from accelerator experiments, searches for dark matter annihilation products, and direct detection of the dark matter particles. This third approach has already eliminated a span of 13 orders of magnitude in mass for Dirac particles and 20 orders of magnitude in their interaction cross section. New direct detection experiments include a search for axions through their conversion to microwave photons in a magnetic field and numerous searches using a variety of scintillators and new types of cryogenic devices to detect nuclei struck by dark matter particles. The latter searches and those attempting to find annihilation products in balloon-borne and large underground detectors now especially seek the supersymmetric neutralino.