Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Proton spin structure and the low-energy pp -> pp eta' reaction   Gluonic degrees of freedom induce a contact term in the effective chiral
Lagrangian description of the low-energy pp -> pp eta' reaction. The strength
of this contact term is, in part, related to the amount of spin carried by
polarised gluons in a polarised proton.

3
The categories of this paper are: physics
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con