Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoproduction of relativistic positronium atoms on extended targets   It is shown that the yield of relativistic positronium atoms in
photoproduction on extended targets is much larger than usually accepted.The
cause of such difference is transparent. At high energies, when the positronium
atom formation time $\tau_f$ becomes greater than the target length L, it is
the free $e^+e^-$ pair that propagates through the target and the formation of
positronium atoms take place out of the target.In the framework of the
light-cone technique we consider the interaction of $e^+e^-$ pair with the
screened Coulomb field of atoms in matter and obtain the analytical expressions
for relativistic positronium atoms photoproduction cross sections on extended
targets.The relations to free pair photoproduction on extended targets are
discussed.

19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
12
The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg