Scientists shine light on whereabouts of antimatter

An international collaboration, including York University, has successfully shone a laser on antimatter atoms to come up with the first successful spectroscopic measurement.

The Big Bang theory requires equal amounts of matter and antimatter to have been created at the beginning of time, but there is little antimatter in the universe now. What happened to all the antimatter is a question scientists from the ALPHA Collaboration, including the ALPHA-Canada group, have spent years trying to to answer. The spectroscopic measurement brings that search one step closer and is considered a major breakthrough.

Professor Scott Menary

“What we were trying to do is compare antihydrogen to hydrogen to see if they have the exact same characteristics,” said York University physics Professor Scott Menary of the ALPHA-Canada group. “Something happened to all the antimatter so that points to there being some slight difference between a matter particle and its antimatter twin.”

The scientists created and trapped antihydrogen atoms in a cryogenically cooled and vacuum-tight cylindrical chamber using a system of magnetic fields. Learning to produce and trap antihydrogen was a huge feat that took six years to accomplish, as matter and antimatter annihilate upon contact. Once they were able to trap the antihydrogen atoms, it took another six years to learn how to shine laser light on them at various frequencies to see what would happen.

Antihydrogen atoms absorb light only at specific frequencies. Precisely measuring the distribution of those absorbed frequencies (spectroscopy) paints a unique fingerprint of the atom. The researchers found that at a specific frequency, the antimatter atoms behaved the same as hydrogen atoms, meaning they both absorbed light at the same frequency.

“Laser measurement on antimatter atoms has been a dream in the field for decades,” said Makoto Fujiwara, TRIUMF research scientist and spokesperson for the ALPHA-Canada group. “We are thrilled and relieved that we finally achieved what we set out to do when we started up in 2004, not least because ALPHA stands for Antihydrogen Laser Physics Apparatus.”

A central challenge was getting the laser system to work in a system cooled to just above absolute zero. The cooling cryostat was designed and built at TRIUMF and the University of Calgary, and its design allowed the researchers the opportunity to try various techniques that ultimately led to the system’s success.

The paper was published Dec. 19 in the journal Nature.

The next experiment in the quest will involve dropping antihydrogen to see if it reacts the same as hydrogen in the gravitational field of the Earth.

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