Decay of positronium

In the case of the positronium spectrum the accuracy is on the MHz-level for most of the studied transitions (Is hyperfine splitting, Is — 2s interval, fine structure) [13] and the theory is slightly better than the experiment. The decay of positronium occurs as a result of the annihilation of the electron and the positron and its rate strongly depends on the properties of positronium as an atomic system and it also provides us with precise tests of bound state QED. Since the nuclear mass (of positronium) is the positron mass and me+ = me-, such tests with the positronium spectrum and decay rates allow one to check a specific sector of bound state QED which is not available with any other atomic systems. A few years ago the theoretical uncertainties were high with respect to the experimental ones, but after attempts of several groups [17,18,19,20] the theory became more accurate than the experiment. It seems that the challenge has been undertaken on the experimental side [13]. 

Another example is dealing with the search for different exotic modes in the decay of positronium [13]. Some of them involve no new particles but violates C and P symmetry, the others are supposed to produce new neutral particles. 

Positron annihilation, namely the decay of positronium atoms e e formed by positron substrate collisions, provides a sensitive probe of critical micelle concentration since the intensity of the slow decay changes abruptly at the c.m.c. Although many workers have been critical of perturbing probes in c.m.c. determination, and particularly of the dye solubilization method, the fluorescence of l-ammonio-8-naphthalene sulphonate give correct c.m.c. values for anionic surfactants. ... 

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