Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutral Pion Lifetime Measurements and the QCD Chiral Anomaly   A fundamental property of QCD is the presence of the chiral anomaly, which is
the primary component of the $\pi^0\rightarrow\gamma\gamma$ decay amplitude.
Based on this anomaly and its small ($\simeq$ 4.5%) chiral correction, a firm
prediction of the $\pi^0$ lifetime can be used as a test of QCD at confinement
scale energies. The interesting experimental and theoretical histories of the
$\pi^0$ meson are reviewed, from discovery to the present era. Experimental
results are in agreement with the theoretical prediction, within the current
($\simeq$ 3%) experimental error; however, they are not yet sufficiently
precise to test the chiral corrected result, which is a firm QCD prediction and
is known to $\simeq$ 1% uncertainty. At this level there exist experimental
inconsistencies, which require attention. Possible future work to improve the
present precision is suggested.

3
The categories of this paper are: physics
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat