Laser spectroscopy of antiprotonic helium and stringent constraint on the antiproton charge and mass

The antiprotonic helium atom-molecule (atomcule in short), (p) over bar e(- ) He2+ = (p) over bar He+, first discovered at KEK and studied in detail at LEAR, is a unique metastable existence interfacing between matter and anti matter. Our recent high-resolution laser spectroscopy of (p) over bar He+ h as reached a precision of 0.5 ppm, and the agreement between our experiment al values of transition energies and the calculations has become better tha n 2 ppm. This agreement in turn sets a severe constraint on the antiproton charge and mass. Future possibilities at the new antiproton decelerator (AD ) are also discussed.