Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First observation of the $\phi\to\pi^+\pi^-\gamma$ decay   Radiative decays of the $\phi$ meson have been studied using a data sample of
about 20 million $\phi$ decays collected by the CMD-2 detector at VEPP-2M
collider in Novosibirsk. From selected $e^+e^-\to\pi^{+}\pi^{-}\gamma$ events
the $\phi\to\pi^{+}\pi^{-}\gamma$ decay has been observed for the first time.
\par Under the assumption that the intermediate $f_{0}(980)\gamma$ state
dominates in the $\phi \to \pi^+\pi^-\gamma$ decay, the corresponding branching
ratio is $Br(\phi\to f_{0}(980)\gamma)=(1.93\pm 0.46\pm 0.50)\times10^{-4}$.
\par Selected $e^+e^-\to\mu^+\mu^-\gamma$ events were used to obtain
$Br(\phi\to\mu^+\mu^-\gamma) =(1.43\pm 0.45\pm 0.14)\times10^{-5}$ for
$E_{\gamma}>20$ MeV. \par Using the same data sample, upper limits at 90% CL
have been obtained for the C-violating decay of the $\phi$:
  $Br(\phi\to\rho\gamma) < 1.2\times10^{-5}$; and for the P- and CP-violating
decay of the $\eta$: \par $Br(\eta\to\pi^+\pi^-) < 3.3\times10^{-4}$.

11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
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The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org