Antimatter Happens, in European Lab

FOR the first tim, scientists have made atoms out of antimatter.

The mirror images of hydrogen atoms, made at the the European Laboratory for Particle Physics (CERN) in Switzerland, lasted only 40-billionths of a second. But the results have given a boost to efforts at making antiatoms in large, longer-lasting amounts and may help resolve one of science's basic puzzles: If the earliest universe had equal amounts of matter and antimatter, why is today's universe dominated by matter?

The creation of antiatoms has been a "Holy Grail" for experimentalists for years, says physicist Lawrence Krauss of Case Western Reserve University in Cleveland. He notes that under current theories, atoms and antiatoms "should react the same under most of the forces of nature. It would be quite remarkable if they behaved differently."

Ordinary atoms consist of electrons, which carry a negative charge, orbiting a nucleus of positively charged protons and neutral neutrons. In the antimatter world, those charges are reversed. But when a particle meets its antiparticle, they annihilate each other in a burst of energy.

For several decades, physicists have been able to make and store antielectrons, known as positrons, and antiprotons, in large particle accelerators. The European team, which announced its results last week, settled on a brute-force approach to bring them together. They created a beam of antiprotons and forced the particles to collide with xenon gas. Many of the antiprotons collided with protons in xenon atoms and were annihilated.

A few annihilations yielded a positron as a byproduct. And an even-fewer number of these positrons joined with an antiproton to form antihydrogen. The three-week experiment last September detected nine antihydrogen atoms.

The results represent "a very nice demonstration that antihydrogen exists," says Gerald Gabrielse, a physicist at Harvard University in Cambridge, Mass. He and other researchers are focusing on other techniques creating antihydrogen, cooling positrons and antiprotons in traps using special magnets, electrical fields, and lasers.

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