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{\bf Abstract Registration Number 566} \\
{\bf Parallel sessions: 5,3} \\
{\bf Plenary sessions: 7,5}
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\abstractheader{\bf Diffractive Dijet Production at HERA \\
H1 Collaboration, DESY}

\abstractbody{
An analysis of interactions of the type 
$ep \rightarrow e X Y$ is presented, where
the component $X$ of the hadronic final state
is well separated in rapidity from a leading baryonic
system with mass $M_{_Y} < 1.6 \ {\rm GeV}$. The magnitude of the
squared four-momentum transferred at the proton vertex satisfies
$|t| < 1 \ {\rm GeV^2}$. Cross sections are presented
for the production of two jets as components of the system $X$, each with
transverse momentum $p_{_T}^{\rm jet} > 5 \ {\rm GeV}$ relative to the 
photon direction in the rest frame of $X$. Results are presented for 
photoproduction and for electroproduction with photon virtualities in the
range $7.5 < Q^2 < 80 \ {\rm GeV^2}$.
At the present level of precision, models based on a factorisable diffractive
exchange with a hard gluon dominated 
structure, evolved to a scale set by the transverse
momentum $\hat{p_{_T}}$ of the outgoing partons
in the hard interaction, 
give good descriptions of the data. 
Exclusive $q \bar{q}$ production, as calculated in perturbative QCD using the 
squared proton gluon density, represents at most a
small fraction of the data.
The possibility of a breaking
of diffractive factorisation due to spectator interactions
is investigated in resolved photoproduction.
}

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