Putting the brakes on antihydrogen. (Physics).

Scientists have long wondered why so little antimatter is found today in the universe. Presumably, both matter and antimatter were created in equal amounts in the Big Bang.

Researchers at the European Organization for Nuclear Research (CERN) in Geneva have now made the first slow-moving atoms of antimatter. By studying them, scientists may more closely compare matter and antimatter and possibly explain the latter's glaring absence.

Well-tested theory holds that every type of particle in matter has an antiparticle with identical mass and spin but opposite electric charge. When such particles meet, the two vanish in a burst of energy.

In the mid-1990s, physicists pieced together the first few atoms of antihydrogen (SN: 1/13/96, p. 20), each of which consists of a negatively charged antiproton orbited by one positively charged antielectron, or positron. Scientists couldn't study their properties, however, because the antiatoms were traveling at nearly light speed and were almost instantly annihilated by contact with matter.

In the new experiment, known as ATHENA, researchers trapped antiprotons in electric and magnetic fields and then mixed them with positrons in an ultracold, jar-size cylinder. In the Oct. 3 Nature, the scientists estimate that they've produced about 50,000 atoms of antihydrogen, which last a few microseconds until they drift into the cylinder's walls and are destroyed, says CERN's Rolf Landua. The ATHENA team now expects to modify its setup in the next year or two to begin laser studies of the antiatoms' properties.--P.W.