Trapping antihydrogen

Trapping antihydrogen. Are there any unexpected differences between matter and antimatter? The international ALPHA collaboration has taken an important step toward answering that question by constructing an apparatus at CERN that can confine freshly made atoms of antihydrogen, the bound state of an antiproton and a positron. (Other groups at CERN are also tackling the trapping problem: See the Quick Study by Gerald Gabrielse, PHYSICS TODAY, March 2010, page 68.) A hot plasma of roughly 10⁴ antiprotons is cooled and introduced into one end of the apparatus, while about 10⁶ low-energy positrons from the decay of radioactive sodium are introduced into the other. Electric fields gently nudge the charged species together in the heart of the device, where they mix at cryogenic temperatures and form antihydrogen. If their kinetic energies are low enough—in temperature units, less than 0.5 K—the antihydrogen atoms are held in the grip of...