Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of $D^0\to \rho^0\gamma$ and search for $CP$ violation in
  radiative charm decays   We report the first observation of the radiative charm decay $D^0 \to \rho^0
\gamma$ and the first search for $CP$ violation in decays $D^0 \to \rho^0
\gamma$, $\phi\gamma$, and $\overline{K}{}^{*0} \gamma$, using a data sample of
943 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy
$e^+e^-$ collider. The branching fraction is measured to be $\mathcal{B}(D^0
\to \rho^0 \gamma)=(1.77 \pm 0.30 \pm 0.07) \times 10^{-5}$, where the first
uncertainty is statistical and the second is systematic. The obtained $CP$
asymmetries, $\mathcal{A}_{CP}(D^0 \to \rho^0 \gamma)=+0.056 \pm 0.152 \pm
0.006$, $\mathcal{A}_{CP}(D^0 \to \phi \gamma)=-0.094 \pm 0.066 \pm 0.001$, and
$\mathcal{A}_{CP}(D^0 \to \overline{K}{}^{*0} \gamma)=-0.003 \pm 0.020 \pm
0.000$, are consistent with no $CP$ violation. We also present an improved
measurement of the branching fractions $\mathcal{B}(D^0 \to \phi \gamma)=(2.76
\pm 0.19 \pm 0.10) \times 10^{-5}$ and $\mathcal{B}(D^0 \to \overline{K}{}^{*0}
\gamma)=(4.66 \pm 0.21 \pm 0.21) \times 10^{-4}$.

16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph