During the last several years, our TRAP collaboration at LEAR, CERN, has pioneered techniques for slowing, trapping, cooling and indefinitely storing antiprotons to energies more than 1010 times lower than previously possible.
The initial comparison of the cyclotron frequencies of antiprotons and protons resulted in a 1000-fold improvement over previous relative mass comparisons. The radio signal from a single trapped antiproton is now being used for precision measurements.
An additional 50-fold improvement in the antiproton to proton mass ratio is expected soon. Many cold antiprotons are "stacked" as another important step toward the eventual production of antihydrogen. Sufficient amounts of positrons have been trapped in vacuum in pursuit of the same goal. The proton-antiproton mass ratio and studies of antihydrogen offer checks of CPT for strongly and electromagnetically interacting particles, respectively.