Spectroscopy of the fundamental few-lepton systems Ps and Ps-

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Precision experiments will be performed on the properties of the purely leptonic fewbody systems Ps- (e+e-e-) and Ps (e+e-), exploiting the unprecedented intensity of the positron source at the FRM II in Garching. The decay rate of Ps- will be measured to an accuracy of about 0.1%, thus allowing for sensitive tests of QED predictions in this fundamental 3-body system. For the first time the photodetachment cross section of Ps- will be measured as well as autoionizing doubly-excited Ps- resonance states, allowing for the first determination of the binding energy of Ps- and a comparison with precise theoretical predictions. Photo-ionization of Ps- will allow to produce a pure, energy-variable 3S1 Ps beam. Using a different Ps production method and the same laser system as for the Ps- excitation, fundamental precision studies on the 1S-2S transition frequency in 3S1 Ps are envisaged, aiming at an improvement of the present best experimental value by an order of magnitude based on the unprecedented intensity of the positron source and the ultra-precise frequency measurement using the frequency comb technology.