Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: $J/\psi \to \gamma\eta'\pi^+\pi^-$ and the structure observed around the
  $\bar pp$ threshold   We analyze the origin of the structure observed in the reaction $J/\psi \to
\gamma \eta'\pi^+\pi^-$ for $\eta'\pi^+\pi^-$ invariant masses close to the
antiproton-proton ($\bar pp$) threshold, commonly associated with the $X(1835)$
resonance. Specifically, we explore the effect of a possible contribution from
the two-step process $J/\psi \to \gamma \bar NN \to \gamma \eta'\pi^+\pi^-$.
The calculation is performed in distorted-wave Born approximation which allows
an appropriate inclusion of the $\bar NN$ interaction in the transition
amplitude. The $\bar NN$ amplitude itself is generated from a corresponding
potential recently derived within chiral effective field theory. We are able to
reproduce the measured spectra for the reactions $J/\psi \to \gamma \bar pp$
and $J/\psi \to \gamma \eta'\pi^+\pi^-$ for invariant masses around the $\bar
pp$ threshold. The structure seen in the $\eta'\pi^+\pi^-$ spectrum emerges as
a threshold effect due to the opening of the $\bar pp$ channel.

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The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: math
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph