SOLUTION OF THE ORTHOPOSITRONIUM LIFETIME PUZZLE

The intrinsic decay rate of orthopositronium formed in SiO2 powder is measured using the direct 2γ correction method such that the time dependence of the pick-off annihilation rate is precisely determined. The decay rate of orthopositronium is found to be 7.0396±0.0012(stat.)±0.0011(sys.)μs-1, which is consistent with our previous measurements with about twice the accuracy. Results agree well with the O(α2) QED prediction, and also with a result reported very recently using nanoporous film.