Anti-Atom Beam Targets Cosmic Mystery: Why Do We Exist?

Image: Antimatter trap

The ASACUSA CUSP apparatus in the CERN Antiproton Decelerator is a tangle of equipment that's used to create, trap and send out particles of antihydrogen. N. Kurodab

Creating an antimatter beam sounds like something only a mad scientist would do, but there's nothing mad about the beam of antihydrogen atoms that scientists generated for the first time at Europe's CERN research center.

The researchers behind the technical achievement, revealed Tuesday in the journal Nature Communications, say the beam could help them shed new light on deep mysteries: Why do we see so much more matter than antimatter in the universe around us? For that matter, why is there a universe at all?

Theoretically, equal amounts of matter and antimatter should have been created in the Big Bang that gave rise to the cosmos as we know it. But as any "Star Trek" fan knows, matter and antimatter annihilate each other in a flash of energy when they interact. Thus, physicists suspect there must have been some subtle difference that allowed matter to dominate the universe.

Previous particle-smashing experiments have provided a smattering of clues as to the difference, but physicists would really like to address the mystery by studying actual anti-atoms. The problem is that it's hard to keep the atoms in existence long enough to make fine-scale measurements.

Actually, antimatter applications have been around for a long time: Hospitals routinely make use of antielectrons, or positrons, to take internal snapshots of our bodies with PET scanners. And researchers are looking into using beams of antiprotons to treat cancer.

But it's only been in the last three years or so that physicists have been able to combine antiprotons and positrons into whole atoms of antihydrogen and hold them inside a specially designed magnetic trap at CERN's Antiproton Decelerator facility on the Swiss-French border. Even then, it's hard to analyze that antihydrogen because the magnetic field that corrals the anti-atoms also interferes with measurements.

In 2012, scientists from CERN's ALPHA collaboration announced that they finally managed to make the first spectroscopic measurements of anti-atoms inside their trap. Now scientists from a different collaboration at CERN, known as ASACUSA, say their apparatus has created a beam of antihydrogen atoms that can be measured more precisely outside the magnetic trap where they were created. At least 80 of the anti-atoms were detected, 2.7 meters (9 feet) downstream of the production region.

Image: Beam setup
This schematic shows ASACUSA's scheme for creating and sending out atoms of antihydrogen. From left to right: The CUSP trap produces the atoms, a microwave cavity (shown in green) induces hyperfine transitions, and a sextupole magnet (shown in red and gray) focuses the beam, sending the atoms to an antihydrogen detector (shown in gold). Stefan Meyer Institut

ASACUSA's apparatus makes use of devices with names that would warm the heart of a mad scientist: a superconducting anti-Helmholtz coil, multiple ring electrodes, a microwave cavity and a beam-focusing spin-selector. The result is that energetic anti-atoms can be guided to a region with a weak magnetic field.

"Antihydrogen atoms having no charge, it was a big challenge to transport them from their trap," ASACUSA team leader Yasunori Yamazaki, a researcher from Japan's RIKEN research center, said in a CERN news release. "Our results are very promising for high-precision studies of antihydrogen atoms, particularly the hyperfine structure, one of the two best-known spectroscopic properties of hydrogen. Its measurement in antihydrogen will allow the most sensitive test of matter-antimatter symmetry."

Yamazaki said his team will resume its experiments this summer with a setup that should produce higher-energy beams of antihydrogen atoms for study. Just wait until the mad scientists get wind of that.