Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Associated production of $\chi_c$ pairs with a gluon in the
  collinear-factorization approach   We calculate cross section for production of $\chi_c$ pairs in proton-proton
collisions. The cross section for the $g g \to \chi_{c J_1} \chi_{c J_2}$ is
considerably smaller (especially for $\chi_{c 1} \chi_{c 1}$ final state) than
that obtained recently in the $k_T$-factorization approach. We calculate
therefore next-to-leading order contributions with $\chi_c$ pair and one extra
associated (mini-)jet. We find these contributions to be much larger than those
for the $2 \to 2$ contribution. Especially the emission of a leading gluon
(carrying a large momentum fraction of one of the incoming gluons) are
important. These emissions in the $k_T$-factorization approach are absorbed
into the initial state unintegrated gluon distributions. A smaller contribution
to the cross section comes from the production of central gluons emitted with
rapidities between the $\chi_c$-mesons. They do lead, however, to an
enhancement of the $\chi_c$-pair production at large rapidity distance between
the mesons. Our present study explains the size of the cross section for the
$\chi_c$ pair production obtained previously in the $k_T$-factorization
approach. Several differential distributions are presented.

12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
1
The categories of this paper are: cs