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Precision Measurement of Orthopositronium Decay Rate Using SiO_2 Powder

Abstract

The intrinsic decay rate of orthopositronium formed in SiO2{\rm SiO_2} powder is measured using the direct 2γ2\gamma 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{\rm SiO_2} powder are used with consistent findings. The intrinsic decay rate of orthopositronium is found to be 7.0396±0.0012(stat.)±0.0011(sys.)μs17.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}, which is consistent with previous measurements using SiO2{\rm SiO_2} powder with about twice the accuracy. Results agree well with a recent O(α2)O(\alpha^2) QED prediction, varying 3.85.63.8-5.6 experimental standard deviations from other measurements.Comment: 16 pages, 7 figures included. To be published in Physics Letters

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