Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Search for the decay $D^{0} \to \pi^{0} \nu \bar{\nu}$   We present the first experimental search for the rare charm decay $D^{0} \to
\pi^{0} \nu \bar{\nu}$. It is based on an $e^+e^-$ collision sample consisting
of $10.6\times10^{6}$ pairs of $D^0\bar{D}^0$ mesons collected by the BESIII
detector at $\sqrt{s}$=3.773 GeV, corresponding to an integrated luminosity of
2.93~fb$^{-1}$. A data-driven method is used to ensure the reliability of the
background modeling. No significant $D^{0} \to \pi^{0} \nu \bar{\nu}$ signal is
observed in data and an upper limit of the branching fraction is set to be
$2.1\times 10^{-4}$ at the 90$\%$ confidence level. This is the first
experimental constraint on charmed-hadron decays into dineutrino final states.

22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat