Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Search for $2\nu\beta\beta$ decay of $^{136}$Xe to the 0$_1^+$ excited
  state of $^{136}$Ba with EXO-200   EXO-200 is a single phase liquid xenon detector designed to search for
neutrinoless double-beta decay of $^{136}$Xe to the ground state of $^{136}$Ba.
We report here on a search for the two-neutrino double-beta decay of $^{136}$Xe
to the first $0^+$ excited state, $0^+_1$, of $^{136}$Ba based on a 100
kg$\cdot$yr exposure of $^{136}$Xe. Using a specialized analysis employing a
machine learning algorithm, we obtain a 90% CL half-life sensitivity of $1.7
\times 10^{24}$ yr. We find no statistically significant evidence for the
$2\nu\beta\beta$ decay to the excited state resulting in a lower limit of
$T^{2\nu}_{1/2}$ ($0^+ \rightarrow 0^+_1$) $> 6.9 \times 10^{23}$ yr at 90% CL.
This observed limit is consistent with the estimated half-life of
$2.5\times10^{25}$ yr.

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The categories of this paper are: funct-an
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The categories of this paper are: stat
12
The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
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The categories of this paper are: q-fin
1
The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: adap-org