Having reported on ways to store and use large amounts of simple antimatter—positrons—we'll now turn our attention to more complex forms of antimatter. While creating positrons is a fairly straightforward process, creating more complex interactions between antiparticles in a controlled fashion is a much more complicated task.

The first talk in this part of the symposium looked at the production of the simplest possible anti-element, antihydrogen. Atomic hydrogen is simple, consisting of one electron orbiting a single proton. Its antimatter equivalent is then a positron orbiting an antiproton. The main hurdle to making it is getting enough of each ingredient (positrons and antiprotons) together in the same place for them to react and form an antiatom.

Gerald Gabrielse spoke about his group's work with the ATRAP collaboration in the creation and study of antihydrogen. To accomplish this, they attempted to create an electric potential trap similar to those used in the storage of positrons. However, their traps had to work in two ways simultaneously: they needed a region that would trap the negative antiprotons and a region that would trap the positively charged positrons, yet these regions have to overlap so that collisions can occur and antihydrogen can (potentially) be formed. They accomplished this using a nested Penning trap, and, in 2008, were producing antihydrogen at a rate of about 20 atoms per hour.

While it's cool to say that you can create antiatoms, there's an obvious question: what can you do with them? Gabrielse spoke about using antihydrogen to test the symmetry that exists between matter and antimatter, and how that was violated often enough to give us a matter-dominated Universe. After discovering that P and then CP symmetries were violated by certain natural processes, physicists current believe that CPT symmetry holds—an antiparticle will have the opposite charge, parity, and time symmetry.

Gabrielse believes that, by studying antihydrogen, which should behave identically to hydrogen if CPT symmetry is correct, he can discover any discrepancies that exist between hydrogen and antihydrogen. The ultimate goal being to study the 1s-2s electron transition in both materials, which would provide one of the most detailed tests to date on if and how matter and antimatter differ.

If you are not content with "simple" antihydrogen and want some antimatter with a non-zero strangeness, then you would need to speak with Dr. Zhangbu Xu of the STAR Collaboration about his work creating antihypernuclei. A hypernuclei is a nucleus—usually made up of protons and neutrons—that contains a hyperon, a baryon that contains a strange quark. The example he talked about was 3 Λ H which is essentially a tritium atom with one neutron replaced by a Λ particle (a Λ particle consists of up, down, and strange quarks).

In the aftermath of gold-gold collisions carried out at Brookhaven's Relativistic Heavy Ion Collider, Dr. Xu and his colleagues found anti-3 Λ H, the heaviest antimatter particle ever created by humans. These particles were seen thanks to their decay path: an anti-3He plus a π+. In addition to finding heavy antimatter, they also found that matter and antimatter—which should be identical in almost every way—are created at different rates. The rate of formation of anti-3He was only half that of 3He, a further route for digging into the reason why our universe is matter-dominated.