Number 79 (Story #3), May 8, 1992 by Phillip F. Schewe and Ben Stein SECOND-GENERATION DETECTORS FOR DARK MATTER are in development. The search for the missing mass will intensify now that the COBE measurements suggest that between 20 percent and 90 percent of the matter in the universe consists of particles or objects that scientists have not yet detected. However, theorists believe that one leading candidate for dark matter, known as a WIMP (for weakly-interacting massive particle), would collide occasionally with ordinary matter. One approach to looking for WIMPs has been to build sensitive detectors, which traditionally measure one of the by-products of nuclear collisions, such as an ionization of electric charge, a flash of light, or the release of a phonon. A problem with these detectors is that it is often very difficult to distinguish signals caused by bona-fide nuclear collisions from those arising from the radioactive decays of detector impurities. However, second generation detectors, being developed independently by a U.S. team at Berkeley and a European team at the University of Rome, will measure two of the by-products. The ratio of energies between the by-products are quite distinct for radioactive decays and nuclear collisions, thereby making it easier to pinpoint a collision of a possible dark-matter particle. (New Scientist, 24 April 1992.)