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{\bf Abstract Registration Number 572} \\
{\bf Parallel sessions: 7,5} \\
{\bf Plenary sessions: 9,7}
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\abstractheader{\bf Diffractive Charmonium Production in Deep Inelastic 
Scattering \\ at HERA\\
H1 Collaboration, DESY}

\abstractbody{
  We present results for the exclusive production of $J/\psi$ and
  $\psi(2S)$ mesons in deep inelastic $ep$ scattering at HERA in the kinematic
  region of the virtuality $2 < Q^2 < 80\:\mbox{GeV}^2$ and the photon proton
  centre-of-mass energy $40 < W_{\gamma^\ast p} < 160\:\mbox{GeV}$.
  $J/\psi$ mesons are detected via their leptonic decays into two muons
  or electrons. The cross section for the reaction $\gamma^\ast p \rightarrow
  J/\psi p$ is evaluated as a function of $Q^2$, $W$ and $t$, and the results
  are compared to phenomenological models. Decay angular distributions are shown.
  The first observation of $\psi(2S)$ mesons in deep inelastic
  scattering at HERA is reported, using the decay mode
  $\psi(2S) \rightarrow J/\psi\:\pi^+\pi^-$. The ratio of the quasi-elastic
  production cross sections for $\psi(2S)$ and $J/\psi$ is extracted
  as a function of $Q^2$.
}

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