Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multiple exchanges in lepton pair production in high--energy heavy ion
  collisions   The recent analysis of nuclear distortions in DIS off nuclei revealed a
breaking of the conventional hard factorization for multijet observable. The
related pQCD analysis of distortion effects for jet production in
nucleus-nucleus collisions is as yet lacking. As a testing ground for such an
analysis we consider the Abelian problem of higher order Coulomb distortions of
the spectrum of lepton pairs produced in peripheral nuclear collisions. We
report an explicit calculation of the contribution to the lepton pair
production in the collision of two photons from one nucleus with two photons
from the other nucleus, $2\gamma + 2\gamma \to \m{l}^+\m{l}^-$. The dependence
of this amplitude on the transverse momenta has a highly nontrivial form the
origin of which can be traced to the mismatch of the conservation of the
Sudakov components for the momentum of leptons in the Coulomb field of the
oppositely moving nuclei.
  The result suggests that the familiar eikonalization of Coulomb distortions
breaks down for the oppositely moving Coulomb centers, which is bad news from
the point of view of extensions to the pQCD treatment of jet production in
nuclear collisions. On the other hand, we notice that the amplitude for the
$2\gamma + 2\gamma \to \m{l}^+\m{l}^-$ process has a logarithmic enhancement
for the lepton pairs with large transverse momentum, which is absent for
$n\gamma + m\gamma \to \m{l}^+\m{l}^-$ processes with $m,n > 2$.
  We discuss the general structure of multiple exchanges and show how to deal
with higher order terms which cannot be eikonalized.

7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin