High-precision spectroscopy of antiprotonic helium - First results from the AD of CERN

New results of the laser and microwave spectroscopy of antiprotonic helium "atomcules" obtained in the first year of operation of the Antiproton Decelerator (AD) facility of CERN are presented. They include the discovery of three new resonant transitions and the determination of the zero-density wavelength of six transitions with an accuracy of 130 ppb in the best case. Auger rates of those states were also determined, and two of them were found to be several orders of magnitude larger than expected from a simple estimate based on the multipolarity Deltal, i.e., the jump in angular momentum required for the antiproton to reach the next lower-lying state of ionized (p) over bar He++. Furthermore, a first signal of a two-laser microwave triple resonance to measure the hyperfine splitting in antiprotonic helium was observed.