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 using high
energy-resolution germanium detectors. As a systematic test, two different
types of SiO2 powder are used with consistent findings. The intrinsic
decay rate of orthopositronium is found to be 7.0396±0.0012(stat.)±0.0011(sys.)μs−1, which is consistent with previous measurements using SiO2 powder with about twice the accuracy. Results agree well with a recent
O(α2) QED prediction, varying 3.8−5.6 experimental standard
deviations from other measurements.Comment: 16 pages, 7 figures included. To be published in Physics Letters