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{\bf Abstract Registration Number 569} \\
{\bf Parallel sessions: 5,4} \\
{\bf Plenary sessions: 7,6}
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\abstractheader{\bf Measurement of Leading Baryon Production at HERA 
  and its \\ Interpretation in terms of Colour Singlet Exchange \\
H1 Collaboration, DESY}

\abstractbody{
Deep inelastic scattering events with an energetic leading baryon have been 
detected by the H1 experiment at HERA using a forward proton spectrometer 
and a forward neutron calorimeter. 
Semi--inclusive cross sections have been measured
in the kinematic region
$2 \le Q^2 \le 50$~GeV$^2$, $0.00006 \le x \le 0.0060$ and
$p_T \le 200$~MeV/c, 
for events with a final state proton with energy 
$740 \ge E^{\prime} \ge 580$~GeV, or
a neutron with energy $E^{\prime} \ge 160$~GeV. The
measurements are used to test production
models and factorization hypotheses. A model of leading baryon production
which consists of pion, reggeon and pomeron exchanges gives a good
description of both semi-inclusive cross sections in the region 
$E^{\prime} / E_p > 0.6$, where $E_p$ is the proton beam energy. This model
is used to constrain the pion structure function.
}

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