Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Search for Heavy Neutrinos in $K^+ \rightarrow \mu^+ \nu_{\mu}$ Decays   The NA62 experiment recorded a large sample of $K^+ \rightarrow \mu^+
\nu_{\mu}$ decays in 2007. A peak search has been performed in the
reconstructed missing mass spectrum. In the absence of a signal, limits in the
range $2 \times 10^{-6}$ to $10^{-5}$ have been set on the squared mixing
matrix element $|U_{\mu4} |^2$ between muon and heavy neutrino states, for
heavy neutrino masses in the range 300-375 MeV/$c^2$. The result extends the
range of masses for which upper limits have been set on the value of $|U_{\mu4}
|^2$ in previous production search experiments.

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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn