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\begin{document}

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\begin{titlepage}

\noindent
\begin{center}
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August 23, 2001 \hspace*{8cm}&
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%                The Structure and Interactions of the Photon},
%                September 2nd-7th 2001, Ascona -- Switzerland} \\
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%                 & Plenary Session  & {\bf ???}   &\\[.7em]
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\vspace*{2cm}

\begin{center}
  \Large
  {\bf 
    Measurement of dijet cross-sections at low 
    {\boldmath $Q^2$} at HERA}

  \vspace*{1cm}
    {\Large H1 Collaboration} 
%     {\Large K.Sedl\'ak}\\
%, J.Ch\'yla, J.Cvach, M.Ta\v{s}evsk\'y, A.Valk\'arov\'a}\\
%  \vspace*{0.5cm}
%     \normalsize Institute of Physics \\
%                      of the \\
%         Academy of Sciences of the Czech Republic
%     (\large Center for Particle Physics, Praha)
\end{center}

\begin{abstract}

\noindent

Triple differential dijet cross-sections in $e^\pm p$ interactions
measured with the H1 detector at HERA are presented in the region
of photon virtuality $2~{\GeV}^2 < Q^2 < 80~{\GeV}^2$, inelasticity 
$0.1<y<0.85$, low transverse jet
momentum $E_t^{jet \hspace{0.5mm}1, 2} > 5~\GeV$, \\
$\overline{E}_t > 6~\GeV$, and
pseudorapidity $-2.5 < \eta^{* \hspace{0.7mm} jet \hspace{0.5mm}1,2} < 0$.
 The data are compared to Monte Carlo
simulations which differ in their assumptions about photon structure
and employ DGLAP or CCFM
parton evolution scheme. Indications of effects connected 
with the resolved
processes of longitudinally polarized virtual photons
are investigated for the first time.

\end{abstract}


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% Control plots

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig1.eps,width=16.0cm}
      \caption{Detector level comparison of the data with HERWIG
        and RAPGAP simulations. Both HERWIG and RAPGAP are
        reweighted to describe the data. All detector level
        selection criteria were applied.}
      \label{velfinal1}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig2.eps,width=16.0cm}
      \caption{Detector level comparison of the data with HERWIG
        and RAPGAP simulations. Both HERWIG and RAPGAP are
        reweighted to describe the data. All detector level
        selection criteria were applied.}
      \label{velfinal2}
    \end{figure}


% Physics plots



    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig3.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of \xg, \Et and $Q^2$. The data are
        compared to HERWIG and RAPGAP MC predictions. 
        Separately shown are the direct (dir) and the resolved
        component of transversally polarized $\gamma$  (res$_T$).}
      \label{qex.fin1}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig4.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of \xg, \Et and $Q^2$. The data are
        compared to HERWIG with an additional contribution of the
        longitudinally polarized photon processes (res$_L$).}
      \label{qex.fin2}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig5.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of \xg, \Et and $Q^2$. The data are
        compared to HERWIG and CASCADE MC, which is based 
        on the CCFM evolution scheme.}
      \label{qex.fin22}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig6.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. Combination of 
        Figure~\ref{qex.fin2} and~\ref{qex.fin22} is plotted here.}
      \label{qex.fin23}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig7.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. The data are
        compared to HERWIG with different $\gamma_T^*$ PDFs.
        $\omega$ is a parameter from the Drees-Godbole factor,
        which suppresses the GRV $\gamma$ PDFs with $Q^2$.}
      \label{qex.fin24}
    \end{figure}




    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig8.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. The data are
        compared to HERWIG and RAPGAP MC predictions. Both
        MC models underestimate the data, especially in
        low \xg and low $y$ range.}
      \label{qx4y.fin1}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig9.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. The data are
        compared to HERWIG with an additional contribution of the
        longitudinally polarized photon resolved processes.
        The additional longitudinal photon contributions
        lead to a better description of the slope of the 
        $y$ distribution.}
%        bring the steepness of the $y$ dependence in the HERWIG 
%        prediction much closer to the measured one.}
      \label{qx4y.fin2}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig10.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. The data are
        compared to HERWIG and CASCADE MC.}
%        CASCADE gives
%        very similar prediction to the sum of direct and
%        transversally polarized resolved processes of HERWIG,
%        however the $Q^2$ dependence is not described very well.}
      \label{qx4y.fin22}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig11.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. Combination of 
        Figure~\ref{qx4y.fin2} and~\ref{qx4y.fin22} is plotted here.}
      \label{qx4y.fin23}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig12.eps,width=16.0cm}
      \caption{Triple differential dijet cross-section as 
        a function of $y$, \xg and $Q^2$. The data are
        compared to HERWIG with different $\gamma_T^*$ PDFs.
        The slope of $y$ distributions are steeper in the
        data than in any of the HERWIG predictions plotted.}
      \label{qx4y.fin24}
    \end{figure}




    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig13.eps,width=16.0cm}
      \caption{Simplified version of Fig.~\ref{qex.fin1} and~\ref{qx4y.fin1}}
      \label{qx4y.sch.fin1}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig14.eps,width=16.0cm}
      \caption{Simplified version of Fig.~\ref{qex.fin2} and~\ref{qx4y.fin2}}
      \label{qx4y.sch.fin2}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig15.eps,width=16.0cm}
      \caption{Simplified version of Fig.~\ref{qex.fin22} and~\ref{qx4y.fin22}}
      \label{qx4y.sch.fin22}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig16.eps,width=16.0cm}
      \caption{Simplified version of Fig.~\ref{qex.fin23} and~\ref{qx4y.fin23}}
      \label{qx4y.sch.fin23}
    \end{figure}

    \begin{figure}[ht]
      \epsfig{file=pict/H1prelim-01-133.fig17.eps,width=16.0cm}
      \caption{Simplified version of Fig.~\ref{qex.fin24} and~\ref{qx4y.fin24}}
      \label{qx4y.sch.fin24}
    \end{figure}


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