Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measuring Polarized Gluon and Quark Distributions with Meson
  Photoproduction   We calculate polarization asymmetries in photoproduction of high transverse
momentum mesons, focusing on charged pions, considering the direct,
fragmentation, and resolved photon processes. The results at very high meson
momentum measure the polarized quark distributions and are sensitive to
differences among the existing models. The results at moderate meson momentum
are sensitive to the polarized gluon distribution and can provide a good way to
measure it. Suitable data may come as a by-product of deep inelastic
experiments to measure $g_1$ or from dedicated experiments.

18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph