In the previous article, I discussed the claim by the ASACUSA experiment at CERN that they had produced the first man-made beam of anti-hydrogren atoms. Now comes the question of what to do with the beam...

Antimatter, first predicted to exist in the 1928 in a research paper by Paul Dirac and experimentally verified in 1932 by Carl Anderson, is in a sense a mirror image of ordinary matter. Antiparticles have the same mass, but opposite electric charge of their ordinary partners. And fundamental symmetries of nature seem to demand that they had identical properties otherwise, that they can only be produced in matter-antimatter pairs, and can only be destroyed in pairs. According to these laws of symmetry, the amount of matter and antimatter produced or destroyed in any process must be identical.

Except the Universe doesn't seem to be aware of this. The entire known Universe seems to be made of ordinary matter (with tiny amount of antimatter produced in high energy reactions, but quickly annihilating again). More precise theories and simulations have indicated that the amount of mass in the known Universe is just a tiny fraction of the amount produced originally, so the asymmetry of matter and antimatter can be small as well, but it still exists and is as yet unexplained. There are numerous theories to explain this discrepancy, but as yet none are experimentally confirmed.

And that is why it is important now to study the properties of anti-matter in greater detail, and to try to find some experimental evidence to explain the matter-antimatter asymmetry and to determine which model is correct. That is one of the goals of the ASACUSA experiment.

The team has announced today that in 2012 they produced a beam of about 80 anti-hydrogen atoms, which they could direct into other experiments. If confirmed, this would be the first such beam of anti-atoms produced by mankind, and the best opportunity yet to study the properties of antimatter.

Now the physicists involved are going to restart their experiment (it was shut down after initial testing just over a year ago) and generate another beam of anti-hydrogen. These anti-atoms will be directed into a small cavity filled with microwave radiation of specific frequencies, and then another magnetic field will separate them into two beams - one which absorbed the radiation and one which didn't. Detectors at the end of the beam will count the numbers in each group. In this way, the hyperfine structure of anti-hydrogen can be determined.

According to quantum mechanics, the electron in a hydrogen atom can only have very specific energies. And when an electron changes to a different orbit, it must either absorb or emit a photon having precisely that energy. This property is so universal, astronomers use it to detect the presence of hydrogen in distant stars and nebulae by looking at the frequency of emitted photons, and comparing it to the spectrum of atoms in the laboratory. And in the case of ordinary hydrogen, these energy levels are known more accurately than almost any other quantity ever measured.

If the matter-antimatter symmetry is unbroken, then anti-hydrogen will display an identical spectrum. The anti-hydrogren atoms in the microwave cavity will absorb photons at the same energy levels, and a large number will be diverted to one detector over the other. If the symmetry is broken at even a small level, then the antihydrogen will be unable to absorb the photons and will travel to the other detector. And by slowly changing the energy of the photons in the cavity, scientists will be able to measure the spectrum of anti-hydrogen.

The results will not be announced for a while, but when they are they will be a major announcement. Either the experiment will find that matter and antimatter symmetry is not exact, breaking a law of nature believed to be exact, or they will discover that it is exact, leading to more speculation about where all of the primordial antimatter has gone. Either way, it will be a stunning result!