Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First test of $O(\alpha ^{2})$ correction of the orthopositronium decay
  rate   Positronium is an ideal system for the research of the bound state QED. New
precise measurement of orthopositronium decay rate has been performed with an
accuracy of 150 ppm. This result is consistent with the last three results and
also the 2nd order correction. The result combined with the last three is
7.0401$\pm0.0007\mu \mathrm{sec}^{-1}$ (100 ppm), which is consistent with the
2nd order correction and differs from the 1st order calculation by 2.6$\sigma$
It is the first test to validate the 2nd order correction.

18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas