A diagram of the RHIC complex at Brookhaven National Lab | Photo Courtesy of Brookhaven National Lab's Flickr
This Friday, April 29th, the Space Shuttle Endeavour will launch into space in search of extremely small particles. Specifically, it will be carrying the Energy Department-supported Alpha Magnetic Spectrometer experiment, which will sweep the skies for signs of antimatter and the even more exotic dark matter.
Why search for something so small in such large a space?
Scientists often work with opposites, since that’s where they sometimes find unexpected answers. Researchers at the Department of Energy’s Brookhaven National Laboratory understand this very well, since they work with the opposite of matter -- antimatter.
Specifically, they used Brookhaven’s Relativistic Heavy Ion Collider (RHIC) -- a supersized demolition derby for extremely small particles -- to observe the heaviest form of antimatter ever seen, the nuclei of antihelium-4 (Read more about it here or go to Nature online).
Nuclei, which consist of protons and neutrons, form the core of an atom. They’re also its heaviest part, with the lighter electrons zipping around its outside.
Adding protons and neutrons adds mass to the nucleus. And smashing heavy nuclei together frees up their constituent parts, which can then recombine into a variety of exotic particles, including the occasional nucleus of heavy antimatter. Scientists studying those atomic-level auto wrecks can learn more about the foundational particles that form our world, and the fundamental forces that drive them.
That’s what RHIC does. It takes gold nuclei (ions), boosts them up to about the speed of light on a 2.4-mile, two-lane racetrack, and crashes them together. But the bigger the antimatter particle, the less likely it is to form. Antihelium-3 didn’t appear until 1970, and it took almost a billion of RHIC’s collisions to produce 18 nuclei of antihelium-4.
A view of the superconducting magnets inside Brookhaven's RHIC | Photo courtesy of Brookhaven National Lab's Flickr
Antihelium-4 might be the opposite of what you’d expect. If you could somehow see it, it would probably look about the same and weigh about the same as regular helium. Rather, a nucleus of antihelium-4 has exactly the opposite charge as regular helium -- rather than being positive, it is negative, so it would move the opposite way in a magnetic field.
Not that there’s much antihelium-4 around -- at least scientists haven’t seen it -- but part of the reason they’re looking for it is that the universe isn’t quite what they expect in this area. According to current theories, the amount of matter and antimatter should be about equal, or at least it should have been when the universe began. Yet we seem to be surrounded by matter, with literally no antimatter in sight.
That’s why Office of Science researchers study the universe. There’s so much still out there for us to understand. And future findings might show that what we think we know about the universe...is in fact, exactly the opposite.
For more information about Brookhaven, visit the Brookhaven National Lab website. Read more about the Department of Energy Office of Science here.