“…One of the motivations driving Ps experimentation, particularly spectroscopic [103,107,228,264,322,377] and lifetime [82,83,163,195] measurements, is that, as a system composed of two low-mass leptons, Ps is an ideal testing ground for QED theory [144]. Precision measurements performed using a wide variety of both hydrogenic and non-hydrogenic atoms, ions, and molecules are, of course, also used for QED tests (e.g.…”