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{\bf Abstract Registration Number 528} \\
{\bf Parallel sessions: 3} \\
{\bf Plenary sessions: 5}
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\abstractheader{\bf Differential (2+1) Jet Rates and Determination 
of $\alpha_s$ in Deep-\\Inelastic Scattering at HERA\\
H1 Collaboration, DESY}

\abstractbody{
Events with a (2+1) jet topology in deep inelastic scattering at HERA 
are  studied in the kinematic range $200 <$ Q$^{2}<$ 10\,000 GeV$^{2}$. 
The rate 
of (2+1) jet events has been determined with the modified JADE jet algorithm 
as a function of the jet resolution parameter and is compared with the 
predictions of Monte Carlo models. In addition, the event rate is 
corrected for both hadronization and detector effects and is compared with 
next--to--leading order QCD calculations. A value of the 
strong coupling constant of 
$\alpha_s(M_{Z}^2)$=$0.118 \pm 0.002
\hspace*{0.2cm} (stat.)
\hspace*{0.2cm} ^{+0.007}_{-0.008} \hspace*{0.2cm} (syst.)
\hspace*{0.2cm} ^{+0.007}_{-0.006} \hspace*{0.2cm} (theory)$ 
is extracted. 
The systematic error includes uncertainties in the calorimeter energy 
calibration, in the description of the data by current Monte Carlo 
models, and in the knowledge of the parton densities. The 
theoretical error is dominated by the renormalization scale ambiguity.
}

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