The ALPHA experiment at CERN hopes to answer one of the most fundamental questions in physics: Why is there more matter than antimatter in the universe? This is a rather troublesome quest to pursue, because antimatter is notoriously difficult to contain – as soon as it touches regular matter, both are annihilated.
Nevertheless, steps are being made to better understand the unusual structure and behavior of antimatter, and a new Nature paper out this week represents the latest success in this regard. Using cutting-edge techniques, an international team of physicists have managed to observe, for the first time, something in antihydrogen – the counterpart to regular hydrogen – named the “hyperfine structure”.
In much the way atoms of matter have electrons orbiting them, antimatter anti-atoms have positrons orbiting them. When these particles and antiparticles are energized, they leap “up” to a higher energy state, and when they lose energy, they fall “down” to a lower energy state.
Seen from a “zoomed out” perspective, this is known as the fine structure; zoomed in to a more precise level, this is known as the hyperfine structure.
This has been observed in regular hydrogen atoms for many decades now, but CERN are now reporting that they’ve observed this in antihydrogen. Apart from the obvious, there was no difference in the hyperfine structures between hydrogen and antihydrogen. In order to get to this point, they first created a fair few antihydrogen anti-atoms through a series of high-energy collisions.
For every million particle collisions at CERN, about four proton-antiproton pairs are created. Using extremely powerful magnetic fields, these antiprotons are then drawn away and brought to the Antiproton Decelerator, which reduces their speed from 96 percent to just 10 percent of the speed of light.
In much the same way one typical hydrogen atom contains just one proton, one antihydrogen anti-atom contains just one antiproton. Isolating these at ALPHA and using precise microwave energy bursts to energetically excite them, the team could observe with remarkable precision the antimatter’s hyperfine structure.
Some have referred to this as the spectral “fingerprint” of antihydrogen, a key identifying feature that no other piece of antimatter displays. Now that it’s been documented, the team will be able to repeat the same experiments for heavier samples of antimatter, including antihelium.
Ultimately, the unfamiliar atomic mirror world to our own will be entirely mapped out by the cartographers of CERN – and perhaps one of the greatest enigmas of our time will be closer to being resolved.