End of the line. An antihydrogen atom in the ATHENA detector decays into pions (yellow) and gamma rays (red).

CERN Gets Antihydrogen in the Can

They're still a long way from powering the antimatter drive of Captain Kirk's Enterprise, but researchers are generating surprising quantities of antihydrogen. Scientists at CERN, the European laboratory for particle physics near Geneva, report in the 19 September issue of Nature that they have produced about 50,000 slow-moving atoms of antihydrogen, the antimatter doppelgänger of the most abundant element in the universe. Because such atoms are very cold and sluggish, the team hopes to study them long enough to probe the fundamental asymmetries between matter and antimatter.

In the past, researchers forged antihydrogen with high-energy accelerators, so the fast-moving atoms quickly flew away and annihilated. CERN physicist Jeffrey Hangst and his colleagues on the ATHENA collaboration at CERN, however, employed a gentler technique. Using a series of magnetic traps, they slowed down antiprotons and antielectrons from thousands of kelvin to about 15 kelvin. When an antiproton decayed into a handful of pions and right nearby, an antielectron became two gamma rays, the researchers inferred that it was the signature of an antihydrogen atom. About such 130 events were detected, suggesting that the group had created about 50,000 cold antihydrogen atoms in all.

Gerald Gabrielse, a Harvard physicist who works on a rival experiment at CERN known as ATRAP, warns that it's easy to be fooled by subtleties of the magnetic traps. But if the result is correct, "it would be an impressive milestone," he says. "It's an initial step, though." Physicists want to use antihydrogen as a tool to see if there is any difference between matter and antimatter. If, for example, hydrogen and antihydrogen absorb different frequencies of light--that is, if their spectra differ--physicists would have to revise a basic assumption about the way matter and antimatter behave.

That will have to wait until they can trap enough of the stuff to tickle it with a laser to figure out its properties. "They're a long way from getting a spectrum," says Gabrielse. And even though few scientists believe that antihydrogen will behave significantly differently from hydrogen, Gabrielse thinks it's vital to test that idea. "Just because our imagination is limited doesn't mean we shouldn't check."

Related site
CERN's antimatter site