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{\bf EPS-HEP99} \\
{\bf Abstract \# 000} \\
{\bf Parallel sessions: 1,2} \\
{\bf Plenary sessions:  1,3}
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\abstractheader{ {\bf
Measurement of Dijet Cross Sections in Deep Inelastic Scattering 
and Determination of the Gluon Density in the Proton   } \\ \\
H1 Collaboration, \\
DESY, Notkestr.85, D-22607 Hamburg, Germany
}

\abstractbody{
Jet cross sections in deep-inelastic scattering have been measured with 
the H1 detector at the positron proton collider HERA. The jets were defined
using the inclusive $k_\perp$ clustering algorithm.
A large kinematical range of four momentum transfers 
$5 < Q^2 < 5000\;\mbox{GeV}^2$, transverse jet energies 
$70 < E^2_{t,jet,Breit} < 3600\;\mbox{GeV}^2$ and
invariant dijet masses $100 < M^2_{jj} < 8000\;\mbox{GeV}^2$
is covered.
The data sample covering $5 < Q^2 < 70\;\mbox{GeV}^2$ was
taken in the years 1996 -- 1997 and corresponds to an integrated luminosity of
${\cal L}_{int} \simeq 20\;\mbox{pb}^{-1}$. For the higher $Q^2$
sample all available positron data (1994 -- 1997) are included resulting
in an integrated luminosity of ${\cal L}_{int} \simeq 36\;\mbox{pb}^{-1}$.
Double differential dijet cross sections have been measured for several sets 
of variables ($Q^2, E_{t,jet,Breit}, M_{jj}, \xi, x_{Bj}$).
The results are compared to perturbative QCD calculations in next-to-leading
order (NLO) of the strong coupling constant. 
Over the whole phase space the next-to-leading predictions give a 
very good description of the data. 
For the low $Q^2$ sample the dependence on the different choices of the 
renormalisation scale are discussed. For $Q^2 > 100$ \mbox{GeV}$^2$,
the gluon density in the proton is determined in a NLO QCD fit to the dijet cross
sections for $0.01 < x < 0.1$ at a scale $\mu^2 = 200$ \mbox{GeV}$^2$.
The result is in good agreement with the gluon density from a QCD analysis
of the H1 structure function data and extends the determination to larger 
$x$.
}
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