Tests of QED with Positronium

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The major emphasis of this research is new and continuing experimental tests of quantum electrodynamics (QED) and relativistic bound-state formalism in the positron-electron system positronium (Ps). Ps is an attractive atom for such tests because it is purely leptonic and because the electron and the positron are antiparticles, and thus the unique effects of annihilation on the real and imaginary energy levels of Ps can be tested to high precision. In the past few years, the precision of QED theory has overtaken that of experiment, and the challenge now is to improve the experimental precision correspondingly and to confront theory. A new measurement of the triplet decay rate will achieve 200 ppm uncertainty early in 2001; the present experiment will push this to a level of 60 ppm.