Precision measurement of orthopositronium decay rate

束缚态QED的二阶修正是在2000年计算的。为了验证束缚态QED的计算和框架，我们进行了正电子衰变率的精确测量。首先，为了克服较大的统计误差，我们研制了适用于高速率测量的新装置。在该装置中，我们采用了YAP闪烁体，这是一种快速的无机闪烁体。我们在以下条件下测量了两次正电子衰变率。*Run I靶：SiO_2气凝胶数据采集周期：2.3个月*Run II靶：SiO_2粉末数据采集周期：3.1个月在两次测量中，我们更换了靶材，以测试材料对测量的影响。每次测量的数据量相当于约130ppm的统计误差。我们在测量中采用了直接拾取校正方法。获得的拾取率，即ANNIHILA…的比率靶材的加入量，RUN I(SiO_2气凝胶)约为3%，RUN II(SiO_2粉末)约为1%。结果发现，两者之间的差异很大。每次测试得到的衰减率为：*RUN I 7.03876+-0.0009(统计)+0.0008-0.0010(系统)μS^-1>*RUN II 7.04136+-0.0009(统计)+0.0007-0.0007(SUN.)μS^-1；合计结果为*RUN I，II 7.0401+-0.0006(σ)+0.0007-0.0009(Sys.)μS^-1&gt；总误差约为150ppm，是世界上最精确的。实测值与1995年以来的三次测量结果一致，也与束缚态QED的O(α^2)计算一致。另一方面，该值与O(α)计算相差约1.7σ。如果我们参考测得的衰减率的世界平均水平，误差达到2.6Gb/σ。因此，可以得出结论，所测得的衰减率支持O(α^2)计算。较少

The second order correction of the bound state QED had been calculated in 2000. To test the calculation and the framework of the bound state QED, we have performed the precision measurement of the Orthopositronium decay rate. First of all, we have developed the new setup suitable for the high rate measurement in order to overcome the large statistic error. In the setup, we have adapted the YAP scintillator, which is the fast inorganic scintillator.We have measured the Orthopositronium decay rate two times in the following conditions.* RUN I target : SiO_2 aerogel data taking period: 2.3 months* RUN II target : SiO_2 powder data taking period: 3.1 monthsIn two measurements, we have changed the target to test the influence of the material on the measurement. The amount of data taken in each measurement corresponds to about 130ppm of the statistic error.We have adapted the direct pick-off correction method in the measurement. The obtained pick-off ratio, which is the ratio of the annihila … More tion in the target material, is about 3% for RUN I (SiO_2 aerogel) and about 1% for RUN II (SiO_2 powder). The difference is found to be large. And it is considered to be come from the difference of the fine structure of the material such as the mean distance between the SiO_2 grains.The obtained decay rates for each run are* RUN I 7.03876+-0.0009 (stat.)+0.0008-0.0010 (sys.) μs^<-1>* RUN II 7.04136+-0.0009 (stat.)+0.0007-0.0007 (sys.) μs^<-1>These are consistent with each other in 1.6σ.The combined result is* RUN I, II 7.0401+-0.0006 (stat.)+0.0007-0.0009 (sys.) μs^<-1>The total error is about 150ppm and the most precious in the world.The measured value is consistent with the three measurements from 1995 and also agreed with the O( α^2) calculation by the bound state QED. On the other hand, the value differs from the O(α) calculation by about 1.7σ. If we refer to the world average of the measured decay rate, the discrepancy reaches 2.6σ. Therefore, one can conclude the measured decay rate supports the O(α^2) calculation. Less