Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First Observation of $P$-odd $\gamma$ Asymmetry in Polarized Neutron
  Capture on Hydrogen   We report the first observation of the parity-violating 2.2 MeV gamma-ray
asymmetry $A^{np}_\gamma$ in neutron-proton capture using polarized cold
neutrons incident on a liquid parahydrogen target at the Spallation Neutron
Source at Oak Ridge National Laboratory. $A^{np}_\gamma$ isolates the $\Delta
I=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} component of the weak
nucleon-nucleon interaction, which is dominated by pion exchange and can be
directly related to a single coupling constant in either the DDH meson exchange
model or pionless EFT. We measured $A^{np}_\gamma = [-3.0 \pm 1.4 (stat) \pm
0.2 (sys)]\times 10^{-8}$, which implies a DDH weak $\pi NN$ coupling of
$h_{\pi}^{1} = [2.6 \pm 1.2(stat) \pm 0.2(sys)] \times 10^{-7}$ and a pionless
EFT constant of $C^{^{3}S_{1}\rightarrow ^{3}P_{1}}/C_{0}=[-7.4 \pm 3.5 (stat)
\pm 0.5 (sys)] \times 10^{-11}$ MeV$^{-1}$. We describe the experiment, data
analysis, systematic uncertainties, and the implications of the result.

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The categories of this paper are: cond-mat
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The categories of this paper are: chem-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-lat
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The categories of this paper are: astro-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: funct-an