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Mysteries of antimatter antihydrogen probed.

Nearly two years ago, the ALPHA project--an international collaboration involving Canadian scientists--announced it had trapped antihydrogen for the first time. The team's latest results, published in Nature, demonstrate for the first time an ability to not only hold on to antihydrogen, but also to probe its properties.

Antihydrogen is made of an antiproton and a positron. Like electrons, positrons have a quantum property called spin which creates a tiny magnetic field that can interact with an external magnetic field. The ALPHA researchers exploited this interaction in order to trap the neutral antihydrogen in a magnetic 'cage.' However, also like electrons, the spin of positrons can be 'flipped' if they are subjected to a high-frequency microwave signal. "This is normally called electron spin resonance; with antimatter we call it positron spin resonance," says Mike Hayden, professor of physics at Simon Fraser University and an ALPHA team member.

Current theories predict that the properties of antimatter should be the same as those for matter, so the ALPHA team hit the antihydrogen with microwave signals at frequencies that would cause a spin flip in a normal hydrogen atom. Sure enough, these frequencies appeared to flip the spin of the positron and eject the antihydrogen from the trap. Signals at different frequencies did not result in antihydrogen ejection.

Although the results were expected, there is still a mystery to be solved. As far as we know, the Big Bang created equal amounts of matter and antimatter, but today's universe contains matter only. One of the goals of the ALPHA project is to look for clues that might explain this asymmetry. "We'll either discover an unexpected difference between matter and antimatter, or we'll confirm our current knowledge and force ourselves to look elsewhere to explain this mystery," says Hayden. "It's exciting either way."

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Title Annotation:FUNDAMENTALS
Author:Irving, Tyler
Publication:Canadian Chemical News
Article Type:Brief article
Geographic Code:1CANA
Date:May 1, 2012
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