Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Azimuthal asymmetries in unpolarized Drell-Yan events on nuclear targets   We show that for Drell-Yan events by unpolarized hadronic projectiles and
nuclear targets, azimuthal asymmetries can arise from the nuclear distortion of
the hadronic projectile wave function, typically a spin-orbit effect occurring
on the nuclear surface. The asymmetry depends on quantities that enter also the
spin asymmetry in the corresponding Drell-Yan event on polarized free nucleonic
targets. Hence, this study can be of help in exploring the spin structure of
the nucleon, in particular the transverse spin distribution of partons inside
the proton. All arguments can be extended also to antinucleon projectiles and,
consequently, apply to possible future measurements involving nuclear targets
at the foreseen HESR ring at GSI.

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The categories of this paper are: hep-ex
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The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: mtrl-th
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: atom-ph