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\begin{document}


\pagestyle{empty}
\begin{titlepage}

\noindent
{\bf  H1-prelim-02-031 \hfill 
  \epsfig{file=/h1/www/images/H1logo_bw_small.epsi,width=2.cm} 
} \\
\noindent April 2002 
\\



\vspace*{3cm}

\begin{center}
  \Large
  {\bf 
        FORWARD $\pi^0$ MESON PRODUCTION AT HERA}\\

  \vspace*{1cm}
    {\Large H1 Collaboration} 
\end{center}

\begin{abstract}
\noindent
The dynamics of QCD evolution at low values of Bjorken-$x$ is studied
via the measurement of hard $\pi^0$ probes which are produced near to the
fragmenting proton direction (the forward region) in deeply inelastic          positron proton scattering at the H1 experiment. Measurements of
 the forward $\pi^0$ cross-section and the accompanying transverse energy flow
 around the $\pi^0$ are presented and used to discriminate between models which
implement different schemes for QCD evolution.
\end{abstract}

\end{titlepage}

\pagestyle{plain}





%-----    FIGURE 1 -----------------------------------------------------------
\begin{figure}[htbp]
\begin{center}
   \epsfig{file=H1-prelim-02-031.fig1.eps,bbllx=0,bblly=0,bburx=567,%
    bbury=567,clip,width=\textwidth}
%       \epsfig{file=H1-prelim-02-031.fig1.eps,width=15cm}
      \caption{
      Inclusive $\pi^0$-meson production cross-sections as a function of $x$
      for $p^*_{T,{\pi}}$ $>$ 2.5 GeV in three regions of $Q^2$. The phase space
      is defined by 0.1 $<y<$ 0.6, $x_{\pi}= E_{\pi}/E_{proton} >$ 0.01, $\theta_{\pi}$
      and $Q^2$ ranges given in the figure. The inner bars are statistical,
      the outer error bars give the statistical and systematical error added
      quadratically. The QCD models based on LO DGLAP parton showers
      with (DIR+RES) and without (DIR) resolved photon processes and on
      the implementation of the CCFM equation are compared to the data.}  
\end{center}
\end{figure}
%------------------------------------------------------------------------------
%-----    FIGURE 2 -----------------------------------------------------------
\begin{figure}[htbp]
\begin{center}
   \epsfig{file=H1-prelim-02-031.fig2.eps,bbllx=0,bblly=0,bburx=567,%
    bbury=567,clip,width=\textwidth}
%       \epsfig{file=H1-prelim-02-031.fig2.eps,width=15cm}
      \caption{
      Inclusive $\pi^0$-meson production cross-sections as a function of $x$
      for $p^*_{T,{\pi}}$ $>$ 3.5 GeV in three regions of $Q^2$. The phase space
      is defined by 0.1 $<y<$ 0.6, $x_{\pi}= E_{\pi}/E_{proton} >$ 0.01, $\theta_{\pi}$
      and $Q^2$ ranges given in the figure. The inner bars are statistical,
      the outer error bars give the statistical and systematical error added
      quadratically. The QCD models based on LO DGLAP parton showers
      with (DIR+RES) and without (DIR) resolved photon processes and on
      the implementation of the CCFM equation are compared to the data.}  
\end{center}
\end{figure}
%-----    FIGURE 3 -----------------------------------------------------------
\begin{figure}[htbp]
\begin{center}
   \epsfig{file=H1-prelim-02-031.fig3.eps,bbllx=0,bblly=0,bburx=567,%
    bbury=567,clip,width=\textwidth}
      \caption{
      Inclusive $\pi^0$-meson production cross-sections as a function of 
      $p^*_{T,{\pi}}$ for $p^*_{T,{\pi}}$ $>$ 2.5 GeV in three regions of $Q^2$.
      The phase space
      is defined by 0.1 $<y<$ 0.6, $x_{\pi}= E_{\pi}/E_{proton} >$ 0.01, $\theta_{\pi}$
      and $Q^2$ ranges given in the figure. The inner bars are statistical,
      the outer error bars give the statistical and systematical error added
      quadratically. The QCD models based on LO DGLAP parton showers
      with (DIR+RES) and without (DIR) resolved photon processes and on
      the implementation of the CCFM equation are compared to the data.}  
\end{center}
\end{figure}
%-----    FIGURE 4 -----------------------------------------------------------
\begin{figure}[htbp]
\begin{center}
   \epsfig{file=H1-prelim-02-031.fig4.eps,bbllx=0,bblly=0,bburx=567,%
    bbury=567,clip,width=\textwidth}
      \caption{ Transverse energy flow around the forward $\pi^0$ for 
      different ranges of $\eta^*_\pi$ in the hadronic CMS as a function
      of the distance from the $\pi^0$ direction. The incoming photon
      direction defines the $+z^*$ direction. The contribution from
      the forward $\pi^0$ is included in the distributions and marked
      on the plots.  
      The phase space
      is defined by 2.0 $< Q^2 < $ 70.0 $GeV^2$, $0.1 <y< 0.6$,
      $x_{\pi}= E_{\pi}/E_{proton} >$ 0.01, $\theta_{\pi}$ and $p^*_{T,{\pi}}$
        ranges given in the figure. The inner bars are statistical,
      the outer error bars give the statistical and systematical error added
      quadratically. The QCD models based on LO DGLAP parton showers
      with (DIR+RES) and without (DIR) resolved photon processes and on
      the implementation of the CCFM equation are compared to the data.} 
\end{center}
\end{figure}
%-----    FIGURE 5 -----------------------------------------------------------
\begin{figure}[htbp]
\begin{center}
   \epsfig{file=H1-prelim-02-031.fig5.eps,bbllx=0,bblly=0,bburx=567,%
    bbury=567,clip,width=\textwidth}
    \caption{ Mean transverse energy  in the region
        $0.5 < \eta^* - \eta^*_{\pi} < 3.0 $ 
      for different ranges of $\eta^*_\pi$ in the hadronic CMS as a function
      of Bjorken $x$. 
      The phase space
      is defined by $2.0 < Q^2 <  70.0$ $GeV^2$, $ 0.1<y< 0.6$,
      $x_{\pi}= E_{\pi}/E_{proton} >$ 0.01, $\theta_{\pi}$ and $p^*_{T,{\pi}}$
        ranges given in the figure. The inner bars are statistical,
      the outer error bars give the statistical and systematical error added
      quadratically. The QCD models based on LO DGLAP parton showers
      with (DIR+RES) and without (DIR) resolved photon processes and on
      the implementation of the CCFM equation are compared to the data.}  
\end{center}
\end{figure}


\end{document}




