The lifetime measurement of orthopositronium

Since the 1989, the precision on the o-Ps lifetime reached a value well under 1000 ppm. Much excitement arose when the measurements performed by the Michigan group did not agree with theory. This problem, called the o-Ps-lifetime-puzzle, ignited much experimental and theoretical activity devoted to its clarification. These are: (1) new direct lifetime measurements by the Tokyo group which did not confirm the discrepancy (2) new theoretical calculations by Adkins et al. including higher order terms improving the theoretical precision well below experimental errors, however, confirming early theoretical estimates (3) searches for exotic decay modes which could explain the lifetime discrepancy at the cost of new physics (violation of basic conservation laws with decays into 1 photon, 2 photons; anomalous rate in 5 photons; millicharged particles; new bosons, ...) (4) exotic suggestions for disappearance mechanisms (mirror worlds, extra dimensions). So far none of these provided a clear solution to the o-Ps-lifetime-puzzle.

Just before the Positronium physics workshop held in Zurich in May 2003, the Michigan group has published a new result which is now in agreement with the theoretical value, somewhat in contradiction with the earlier results from the same group. The easy shortcut is to assume that the o-Ps-lifetime puzzle is closed. Should we however indeed consider that the o-Ps lifetime puzzle is solved and hence assume that further precise measurements of positronium (o-Ps lifetime, ...) are irrelevant?

A new high precision experiment

The lifetime (or decay rate) of the ortho-positronium (o-Ps) is measured by presently running experiments with an error which is at least two order of  magnitude bigger than the error on the theoretical value predicted by the QED theory, including higher order corrections.
We intend to measure the orthopositronium decay rate in vacuum with the highest possible precision to test QED predictions to check this corrections.

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