Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Semihard diffractive production of neutral mesons by off shell photons
  and the range of pQCD validity   We study the dependence on photon virtuality $Q^2$ for the semihard
quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or
real photon (at $s\gg p_{\bot}^2, Q^2; p_{\bot}^2 \gg \mu^2 \approx (0.3$
GeV)$^2$). To this end we calculate the corresponding amplitudes (in an
analytical form) in the lowest nontrivial approximation of the perturbative
QCD. The amplitudes for the production of mesons consisting of light quarks
vary very rapidly with the photon virtuality near $Q^2=0$.
  We estimate the bound of the pQCD validity region for such processes. For the
process with mass shell photon the obtained bound is very high, and this region
seems beyond opportunities of real experiment. This bound decreases fast with
the increase of $Q^2$, and we expect that the virtual photoproduction at HERA
provides the opportunity to test the pQCD results. The signature of this region
is discussed.

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The categories of this paper are: plasm-ph
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: hep-lat