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\begin{titlepage}


\noindent
\begin{flushleft}
{H1prelim-02-065}\\
{{\today}} \hspace*{14cm}\vspace*{-1cm}\epsfig
{file=/h1/www/images/H1logo_bw_small.epsi,width=2.cm}
\end{flushleft}
\vspace*{2cm}
\begin{center}
  \begin{Large}                   
  {\bf Search for Anomalous Single Top Quark Production}\\
  {\bf at HERA}\\
  {\bf Update of the Hadronic Channel}

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


% --- Abstract

\begin{abstract} \noindent

A search for anomalous top quark production mediated by a flavour changing neutral current via a gamma-u-t coupling is performed in $e^\pm p$ collisions at HERA. The search exploits data collected from 1994 to 2000 and is motivated by the previous observation of outstanding events with isolated leptons, missing transverse momentum and a jet with large transverse momentum. Following a corresponding analysis in the leptonic channel we here present the search for top decays into a b-jet and a W-boson, which decays hadronically. The data is compared to the Standard Model expectation and to an anomalous top production model.  No excess is found in the data. Leptonic and hadronic decay modes are combined and an upper limit on the anomalous gamma-u-t coupling is established in a region of parameter space not excluded by other experiments at LEP and TEVATRON. 

\end{abstract}

\end{titlepage}



\pagenumbering{arabic}

\vfill
\clearpage


% --- control distributions (basic 3jet selection)

\begin{figure}[p] 
  \begin{center}
     \epsfig{file=H1prelim-02-065.fig1.eps,width=16cm}
  \end{center}
  \caption{Control plots for the 3-jet sample ($P_T^{jet} > 25,20,15$~GeV) in 1994-2000 data.}
  \label{}
\end{figure} 

\vfill
\clearpage

% --- high E_T selection and discriminating variables

\begin{figure}[p] 
  \begin{center}
     \epsfig{file=H1prelim-02-065.fig2.eps,width=16cm}
  \end{center}
  \caption{Observables used for top / SM discrimination in the high $E_T$ sample ($E_{T,tot}>110$~GeV, $P_T^{jet}>40,25,20$~GeV). A top ansatz is used assigning the two jets with an invariant mass closest to 80~GeV to the $W$  ($W$ combination) and the remaining high-$P_T$ jet to the $b$-quark ($b$-jet candidate) from the top decay. The angle $\theta^\star$ denotes the angle in the top system between the two jets forming the $W$ combination. The top Monte Carlo is displayed in arbitrary normalization.}
  \label{}
\end{figure} 

\vfill
\clearpage

% --- list of top cuts

\Large
\underline{Top Cuts:}
\begin{itemize}
 \item W mass window: \qquad \ $70$~GeV $<M^{2 jet}_{W comb.}<90$~GeV
 \item Top mass window: \quad  $150$~GeV $<M_{jets}<210$~GeV
 \item Angular cut: \qquad \qquad cos $ \Theta^* >-0.5$
\end{itemize}                
\vspace*{1.5cm}

% --- distributions after certain top cuts

\begin{figure}[h]
\begin{center}
 \epsfig{file=H1prelim-02-065.fig3.eps,width=15cm}
\end{center}   
 \caption{Distributions of the decay angle~cos~$\theta^\star$, the invariant mass of all jets, and the invariant 2-jet mass of the the $W$ combination in the high $E_T$ sample after cuts on the other variables.}
  \label{}
\end{figure}

\vfill
\clearpage

% --- table with number of observed and expected events after top cuts 

\begin{table}[ht]
\begin{center}
\Large
H1 Preliminary\\[0.3cm]
\begin{tabular}{|c|c|}
\hline 
                                      & After Top Cuts   \\ \hline
$Data$                                & $14$             \\ \hline
$SM$                                  & $19.6 \ \pm 7.8$ \\ \hline
Efficiency ($t\rightarrow 3 \ jets$)  & $27\%$           \\ \hline

\end{tabular}\\[1cm]
\end{center}
  \caption{Number of observed and expected events in the hadronic top selection  (high $E_T$ sample after all top cuts) of 1994-2000 data.}
  \label{}
\end{table}

\vspace*{2.5cm}


% --- top mass after all top cuts

\begin{figure}[h] 
  \begin{center}
     \epsfig{file=H1prelim-02-065.fig4.eps,width=9cm}
  \end{center}
  \caption{Reconstructed top mass after all top cuts. The top Monte Carlo is displayed in arbitrary normalization.}
  \label{}
\end{figure} 


\vfill
\clearpage

%--- table with exclusion limits on cross section and coupling

\vspace*{-2cm}
\begin{table}[h]
\begin{center}
\Large
H1 Preliminary\\[0.3cm]
\hspace*{-1.cm}
\begin{tabular}{|c|c|}
\hline 
                                     & Exclusion Limit at 95\% CL                     \\[0.2cm] \hline
Hadronic Channel                     & $\sigma_{top}$($\sqrt{s}=320$~GeV)$ < 0.40$~pb                 \\[0.2cm] \hline
Combined (Hadronic+Leptonic Channel) & $\sigma_{top}$($\sqrt{s}=320$~GeV)$ < 0.43$~pb \\ 
                                     & $\kappa_{\gamma,u} < 0.22$                     \\ \hline

\end{tabular}\\[1cm]
\end{center}
  \caption{Exclusion limits on the cross section for anomalous top production at HERA and on the $tu\gamma$ coupling $\kappa_{\gamma,u}$.}
  \label{}
\end{table}

\vspace*{1.5cm}

%--- exclusion limit plot

\begin{figure}[h] 
  \begin{center}
     \epsfig{file=H1prelim-02-065.fig5.eps,width=12.cm}
  \end{center}
  \caption{Exclusion limits at 95\% CL on the anomalous $tq\gamma$ magnetic coupling $\kappa_\gamma$ and the vector coupling $v_Z$ obtained at the TEVATRON, LEP and HERA colliders. The H1 limit applies to the coupling $\kappa_{\gamma,u}$ to the $u$-quark only. Both the H1 limit for leptonic decays and the H1 combined limit for leptonic and hadronic decays of the top quark are indicated.}
  \label{}
\end{figure} 


% --- references 

\begin{thebibliography}{99}
\normalsize
\bibitem{budapest}
H1 Collaboration, 
``Search for Single Top Production in $e^\pm p$ collisions at HERA'', \\ 
contributed paper 824, EPS2001, Budapest
\end{thebibliography}  

\end{document}







