Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of Beam Spin Asymmetries in the Process $e p \rightarrow e
  \pi^{+}\pi^{-}X$ with CLAS12   The observation of beam spin asymmetries in two-pion production in
semi-inclusive deep inelastic scattering off an unpolarized proton target is
reported. The data presented here were taken in the fall of 2018 with the
CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron
beam delivered by CEBAF at JLab. The measured asymmetries provide the first
opportunity to extract the parton distribution function $e(x)$, which provides
information about the interaction between gluons and quarks, in a collinear
framework that offers cleaner access than previous measurements. The
asymmetries also constitute the first ever signal sensitive to the
helicity-dependent two-pion fragmentation function $G_1^\perp$. A clear sign
change is observed around the $\rho$ mass that appears in model calculations
and is indicative of the dependence of the produced pions on the helicity of
the fragmenting quark.

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The categories of this paper are: acc-phys
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: physics