Sub-ppm Laser Spectroscopy of Antiprotonic Helium and a CPT-Violation Limit on the Antiprotonic Charge and Mass

Six laser-resonant transitions have been detected in metastable antiprotonic helium atoms produced at the CERN Antiproton Decelerator. They include UV transitions from the last metastable states in the v=n- ell-1=0 and 1 cascades. Zero-density frequencies were obtained from measured pressure shifts with fractional precisions between 1.3 x 10-7 and 1.6 x 10-6 . By comparing these with QED calculations and the antiproton cyclotron frequency, we deduce that the antiproton and proton charges and masses agree to within 6 x 10-8 with a confidence level of 90%