New measurement of the orthopositronium decay rate

The orthopositronium decay rate is measured with an entirely new method, in which the pickoff annihilation rate is directly measured as a function of time with a high-resolution germanium detector. The decay rate can be determined without the ambiguities of the thermalization nor of the extrapolation, which might have been sources of the main systematic errors in all the previous experiments. Two independent measurements are carried out with two different types of SiO2 powder, resulting in decay rate values consistent with each other. The combined result is λ0 = 7.0398 ± 0.0025 (stat.) ± 0.0015 (sys.) μs−1, which is consistent with the QED prediction, and differs by 2.9–4.1Φ from three recent measurements.