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{\bf EPS-HEP99} \\
{\bf Abstract \# 000} \\
{\bf Parallel sessions: 2,5} \\
{\bf Plenary sessions: 3,5}
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\abstractheader{ {\bf
\boldmath Measurement of $D^{\ast}$ Meson Cross Sections at HERA
and Determination of the Gluon Density in the Proton using NLO QCD } \\ \\
H1 Collaboration, \\
DESY, Notkestr.85, D-22607 Hamburg, Germany
}
\abstractbody{
With the H1 detector at the $ep$ collider HERA,
$D^{\ast}$ meson production cross sections
have been measured
in deep inelastic scattering
with four-momentum transfers $Q^2>2$ GeV$^2$
and in photoproduction at energies around
$W_{\gamma p}\approx 88$ GeV and $194$ GeV.
Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical
and experimental uncertainties.
Using these calculations,
the NLO gluon momentum distribution in the proton,
$x_g g(x_g)$, has been extracted
in the momentum fraction range $7.5\cdot 10^{-4}< x_g <4\cdot 10^{-2}$
at average scales $\mu^2 =$ 25 to 50 GeV$^2$.
The gluon momentum fraction $x_g$
has been obtained
from the measured kinematics of the scattered electron and the
$D^{\ast}$ meson in the final state.
The results compare well with the gluon distribution obtained from
the analysis of scaling violations of the proton structure function $F_2$.
}
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{\bf References }\\
1. H1 Collaboration, C.~Adloff {\it et al},
DESY-98-204 / submitted to Nucl. Phys. B
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