  Antiprotonic helium, a neutral exotic three-body system consisting of a
helium nucleus, an electron and an antiproton, is being studied at the
Antiproton Decelerator of CERN by the ASAUCSA collaboration. Using laser
spectroscopy of the energy levels of the antiproton in this system and
comparison to theory, a value of the antiproton-to-electron mass ratio with an
error of 3 ppb could be obtained. This result agrees with the most precise
measurement of the value of the proton and allows us to extract a limit of the
equality of the proton and antiproton charge and mass of 2 ppb. Using microwave
spectroscopy, the hyperfine structure of antiprotonic helium has been measured
to 30 ppm. Experimental improvements are expected to soon provide a new value
for the magnetic moment of the antiproton.
