Number 98 (Story #2), October 13, 1992 by Phillip F. Schewe and Ben Stein PRODUCING ANTI-HYDROGEN is the aim of several experiments. The first step, creating positrons and antiprotons, is difficult enough, but forming a stable anti-atom out of the anti-particles seems harder still. Gerald Gabrielse of Harvard uses the Low Energy Antiproton Ring (LEAR) at CERN plus his own electrostatic trap to slow (and store) antiprotons down to energies as low as 0.3 meV. Bringing them together with positrons (perhaps in a double-trap setup) is several years off. At Fermilab, Charles Munger of SLAC hopes to search for the very few anti-hydrogen atoms he suspects may be generated when a beam of antiprotons, striking a hydrogen target, creates electron-positron pairs; occasionally the positron might link up with one of the antiprotons. One direct approach involves colliding antiproton and positron beams together but, according to Gabrielse, this would most likely result in the particles bouncing off each other rather than mating. Scientists expect that anti-hydrogen, once it can be made, will be useful in the study of gravity and quantum mechanics. (Science, 25 Sept. 1992.)