Scientists would like to learn more about antimatter to see if it behaves differently from matter in a way that could help solve the puzzle of why the universe has so little antimatter.
One key set of experiments would involve shining lasers on antimatter atoms, which can absorb and emit light much like atoms of regular matter. If antihydrogen atoms emitted a different spectrum of light than hydrogen atoms, such spectral differences could yield insights on other ways matter and antimatter differ, the researchers said.
Now, for the first time, scientists have used lasers to carry out a spectral analysis of antihydrogen atoms.
"I like to call this the Holy Grail of antimatter physics,"said study co-author Jeffrey Hangst, a physicist at Aarhus University in Denmark. "I've been working for more than 20 years to make this possible, and this project has finally come together after many difficult steps."
The researchers experimented with antihydrogen, which is the simplest atom of antimatter, just as hydrogen is the simplest atom of regular matter. Antihydrogen atoms each consist of one antiproton and one positron.
Creating enough antimatter for researchers to examine has proven highly challenging. To create antihydrogen atoms, the researchers mixed clouds of about 90,000 antiprotons with clouds of about 1.6 million positrons (or antielectrons), yielding about 25,000 antihydrogen atoms per attempt using the ALPHA-2 apparatus, which is an antimatter generation and trapping system, at the European Organization for Nuclear Research (CERN) in Switzerland.
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After the researchers create the antihydrogen atoms, "you have to hold on to them, and that's very difficult," Hangst told Live Science. Antihydrogen is electrically neutral, which means that it cannot be held in place using electric fields, "and you have to keep it away from matter, so it has to be kept in high vacuum," he said. In addition, antimatter is best kept at temperatures close to absolute zero (minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius), so it is slow-moving and easier to hold on to than antihydrogen atoms.
The researchers trapped antihydrogen in very strong magnetic fields. "We can now hold about 15 antihydrogen atoms at a time," Hangst said.
Then, they shone a laser on the antihydrogen, which caused the atoms to give off light. The scientists then measured the spectrum of light that antihydrogen gave off with a precision of about a few parts in 10^10 - that is, a 1 with 10 zeroes behind it. In comparison, researchers can currently measure these properties of hydrogen to a precision of a few parts in 10^15. "We want to measure antihydrogen with the same precision as hydrogen, and we see no reason why we can't do that in the future," Hangst said.
Currently the spectrums of light from hydrogen and antihydrogen look alike.
However, measuring antihydrogen with greater precision might ultimately reveal differences between matter and antimatter that could solve the mystery of the missing antimatter and lead to revolutionary changes in the Standard Model. "This is really game-changing work," Hangst said.
The scientists detailed their findings online Dec. 19 in the journal Nature.