Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chi_2 production in polarized pp collisions at RHIC: measuring \Delta G
  and testing the color octet model   We consider the production and decay of the $\chi_2$ charmonium state in
polarized and unpolarized $pp$ collisions at RHIC in the framework of an
effective theory based on the QCD multipole expansion. We find that the angular
distribution in the decay of the produced charmonium, $\chi_2 \to J/\psi +
\gamma$, in the unpolarized case allows us to distinguish clearly between the
color singlet and color octet production mechanisms. Once the production
mechanism is known, the angular distribution in the polarized case can be used
to measure the polarized gluon distribution in the proton, $\Delta G(x)$.

22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs