Antiproton mass measurements

The most accurate mass measurements by far are measurements of charge-to-mass ratios, with the assumption that there is only one fundamental unit of charge. The most accurate of such antimatter mass measurements, by orders of magnitude, is an extremely high precision comparison of the charge-to-mass ratio of the antiproton and proton. Mass measurements with antimatter particles require the solution of unique problems-owing to the need to obtain the antimatter from unusual sources, and because antimatter particles annihilate upon interacting with matter. For the future, the most accurate antimatter mass measurements are likely to arise from even more accurate comparisons of the frequency of laser transitions of antihydrogen and hydrogen. The techniques to slow, trap and cool antiprotons that were developed to make the q/m measurements possible, have now made it possible to produce slow antihydrogen, an important step toward the eventual laser spectroscopy of antihydrogen. (C) 2006 Elsevier B.V. All rights reserved.