Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two photon width of eta_c   We discuss the measured partial width of the pseudoscalar charmonium state,
$\eta_c$, into two photons. Predictions from potential models are examined and
compared with experimental values. Including radiative corrections, it is found
that present measurements are compatible both with a QCD type potential and
with a static Coulomb potential, with $\alpha_s$ evaluated at two loops.
Results are also compared with those from $\jpsi$ data through the NRQCD model.

17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn