June 6, 2011

Physicists Get Best Look Yet At Antimatter

In a study published in the journal Nature Physics, researchers report trapping some 300 antihydrogen atoms for a record 16 minutes, a stunning technical feat that promises deeper insights into the mysteries of antimatter.

Particles and anti-particles annihilate each other in a small flash of energy when they collide making the study of them extremely difficult.

Fourteen-million years ago, at the moment of the big bang, matter and antimatter are believed to have existed in equal quantities. If that balance had persisted, the universe as we know it would never have come into being.

Luckily for us, nature seemed to have a slight preference for matter, and today antimatter has so far proven to be rare. This asymmetry remains one of the so far unsolved mysteries in particle physics but ongoing low-energy experiments with hydrogen atoms could be a key step toward solving that puzzle.

"We can keep the antihydrogen atoms trapped for 1,000 seconds. This is long enough to begin to study them -- even with the small number that we can catch so far," Jeffrey Hangst, spokesman for the ALPHA team conducting the tests at the European Organization for Nuclear Research (CERN) in Geneva, told the AFP news agency.

Researchers at the CERN high-energy accelerator have created antihydrogen atoms, and then chilled them to near-zero temperatures. The next goal is to use laser and microwave spectroscopy to compare the frozen particles to their normal hydrogen counterparts.

Physicists last fall succeeded in trapping dozens of antimatter atoms and holding them in place for a fraction of a second, a world first at the time. But that was not long enough for the volatile particles to settle into the stable "ground" state needed for precise measurements.

This recent capability extends storage time 5,000 fold, making it possible to carry out crucial experiments such as looking for "violations" or discrepancies in something called the charge-parity-time reversal (CPT) symmetry.

This CPT symmetry says that a particle moving forward through time in our universe should be indistinguishable from an antiparticle moving backwards through time in a mirror universe. In other words, the hydrogen and antihydrogen should have exactly the same spectral profile.

"Any hint of CPT symmetry breaking would require a serious rethink of our understanding of nature," Hangst in a statement. "But half the universe has gone missing, so some kind of rethink is apparently on the agenda."

Plans to measurement the antihydrogen are due to begin underway shortly, and could yield results before the end of the year. "If you hit the trapped antihydrogen atoms with just the right microwave frequency, they will escape from the trap and we can detect the annihilation," Hangst said. "It will be the first time anybody has interacted with anti-atoms to probe their structure."

The ability to store bits of antimatter for a quarter of an hour could also provide a new way to measure how they are influenced by gravity, Hangst added.


Image 1: This is an artistic representation of the ALPHA neutral antimatter trap, suggesting the nature of the ALPHA apparatus as a container for antihydrogen. Credit: Chukman So, copyright © 2011 Wurtele Research Group

Image 2: In an antihydrogen atom (top), a positively charged antielectron, or positron, orbits a negatively charged antiproton: the mirror image of an ordinary hydrogen atom (bottom). Credit: Chukman So, copyright © 2011 Wurtele Research Group

Image 3: This is an artist's image of the ALPHA trap which captured and stored antihydrogen atoms. Credit: Chukman So, copyright © 2011 Wurtele Research Group


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