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\begin{document}

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\begin{titlepage}

\noindent
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%{\it {\large version of \today}} \\[.3em] 
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%Submitted to & \multicolumn{3}{r}{\footnotesize Electronic Access: {\it http://www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em] \hline 
%Submitted to & \multicolumn{3}{r}{\footnotesize {\it www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em] \hline 
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\multicolumn{4}{l}{{\bf
                 14th International Workshop on Deep Inelastic Scattering,
                 DIS2006, April 20-24, 2006, Tsukuba, Japan}} \\
%                 & Abstract:        & {\bf xx-xxx}    &\\
%                 & Parallel Session & {\bf x}   &\\ \hline
 & \multicolumn{3}{r}{\footnotesize {\it
    www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em]
 & \multicolumn{3}{r}{H1prelim-06-064} \\[.2em]
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\vspace*{2cm}

\begin{center}
  \Large
  {\bf 
    Search for Events with Isolated Tau-Leptons \\  
    and Missing Transverse Momentum at HERA \\ 
%    {\boldmath $e q$} 
    }

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

\begin{abstract}

\noindent
A search for the production of tau leptons in $ep$ collisions 
with the H1 detector at HERA is presented. A total integrated 
luminosity of 287 pb$^{-1}$ taken in the years 1994-2005 is analysed,
which includes recent data collected in the period 2003-2005 (HERA-II), 
where 51 pb$^{-1}$ of $e^+p$ data and 111 $e^-p$ data were taken.
Tau leptons are identified by using an 
identification algorithm based on the search for isolated charged
tracks associated to narrow hadronic jets detected in the 
calorimeters, a typical signature of the one-prong hadronic tau decay. 
In the region where the hadronic system ($X$) has a transverse
momentum $P_T^X > 25 \,\GeV$ 3 events are observed in the data where the
Standard Model (SM) expectation is  0.74$\pm$0.13 events.

\end{abstract}


\end{titlepage}

\pagestyle{plain}

\section{Introduction}

The preliminary results presented here are an update of the recently
published search for events with tau leptons and missing transverse
momentum ($P_{T}^{{\rm miss}}$) in HERA-I data included in the paper on 
tau lepton production in $ep$ collisions \cite{tauHERA1}. 
The selection is shown in table 1.
This search complements the observation of isolated electrons and muons 
in events with missing transverse momentum \cite{eps05Results}, 
\cite{isolAndreev2003}.

% 
% \section{Standard Model Processes}
% 
% The sum of all processes mentioned in this section is named {\bf SM prediciton}.
% In the SM, genuine tau leptons may originate from the following processes:
% 
% \begin{itemize}
% 
% \item SM $W$-Production
% 
% There are several diagrams that can create real $W$-Bosons in $ep$-collisions.
% Mainly, the $W$-bosons can be radiated off the scattered quark.  
% The EPVEC Monte Carlo generator was used to model the process. 
% The cross section at HERA is about 1 pb. 
% This process is denoted as {\bf SM Signal} in the following.
% 
% \item Tau Pair Production
% 
% Tau pairs are generated mainly via photon-photon collisions. The
% GRAPE Monte Carlo generator was used to model this process and production
% of electron and muon pair production. The cross section
% is about 20 pb for $P_{T}^{\tau} > 2 \GeV$ but it falls steeply with $P_T^\tau$.  
% Its contribution to the final sample is negligible. The same is true for the
% production of electron and muon pairs also simulated by GRAPE, 
% which contribute by misidentification of electrons or muons as tau leptons.
% 
% Additionally to these SM processes the signature of possible BSM events was
% by the ANOTOP MC generator which simulates the production of single 
% $top$-quarks through FCNC. 
% The analysis was balanced between suppression
% of SM background and acceptance of EPVEC and ANOTOP events.
% 
% 
% \end{itemize}
% 
% The following Standard Model processes do not include genuine tau leptons
% but contribute to the selected sample due to mismeasurements and are hereforth
% denoted {\bf SM background}:
% 
% \begin{itemize}
% 
% \item Charged Currents in Deep Inelastic Scattering (CC DIS)
% 
% CC DIS was modeled with the RAPGAP MC generator.
% Genuine missing transverse momentum $P_T^{miss}$ from the neutrino and one (or more) QCD jets from the scattered quark (and eventual higher order processes) misidentified as $\tau$-lepton make this SM process the largest background for this search.
% 
% \item Neutral Currents in Deep Inelastic Scattering (NC DIS)
% 
% The RAPGAP MC generator was used to model NC DIS at $Q^2 > 60 \GeV$.
% Fake $P_T^{miss}$ from fluctuations in the energy measurement and misidentification
% of the scattered electron as $\tau$-lepton make this process enter the final sample.
% 
% \item Photoproduction of Jets
% 
% Jets produced in photoproduction can enter the final sample if missing energy
% is measured due to fluctuations of the detector response and narrow
% jets are misidentifed as $\tau$-leptons. The PYTHIA MC generator was used to 
% model the production of jets in photoproduction for Q$^2 < 4 \GeV$. Since
% the exact cross section is not known, the MC expectation was scaled to
% an inclusive selection of jets in photoproduction.
% 
% \end{itemize}
% 
% \section{Analysis method}
% 
% The selection is based on the selection of narrow jets with one associated 
% track in an inclusive CC-like sample. The cuts are summarized in table 1. 
% Selection of the final sample begins with an inclusive CC DIS selection.
% Comparing with the selection used in the measurement of the CC DIS 
% cross-section certain cuts, mainly the one on the HFS imbalance $V_{ap}/V_{p}$ 
% were relaxed to optimize acceptance of W and a possible signal from 
% single-$top$-production.
% 
% For selection of the final sample, the presence of at least one tau-jet 
% candidate was required. Strict isolation criteria against other jets and 
% leptons and the requirement of acoplanarity are used to severly reduce 
% SM background and remaining non-$ep$-background. The last cut is the most 
% severe cut requiring the isolation of the track in the $tau$-candidate jet 
% against other tracks in a cone of 1.0 in the $\eta\phi$-plane.
% 
% To control size of the SM background samples for the 
% contributing processes were selected inclusively and in the phasespace 
% $P_T^{miss} > 12 \GeV$ and the description of $\tau$-jet candiates  studied.
% 
% \section{Results}
% 
% The analysis of HERA-II $e^+p$ data collected from October 2003 to August 2000 
% yields 3 events in the final sample where 0.74 are expected in the SM prediction.
% The respective yield in HERA-II $e^-p$ data collected from December 2004 to October 2005 is ... events selected for ... expected.
% The SM Prediction is dominated by CC DIS. The mean cross section for this process
% is about a factor two higher in $e^-p$ than in $e^+p$.
% 
% Table 2 shows a summary of H1 e+p data, e-p data and the full H1 $e^{+-}p$ data set.
% 
% 
% \section{Summary}
% 
% A search for events containing isolated $\tau$ leptons and significant missing
% transverse momentum produced in $e^{\pm}p$ collsions is performed with the H1
% detector at HERA in the period 1994-2005.
% The analysed data sample corresponds to an integrated luminosity of 278 pb$^{-1}$
% A total of 25 events are observed in the data, compared to an expectation
% of 24.3 $\pm$ 4.6. At large hadronic transverse momentum 
% $P_T^X > 25 \GeV$ a total of 3 events are observed in the data where the
% Standard Model (SM) expectation is only 0.74$\pm$0.14 events. All 3 of
% these events are observed in the 2004-2005 $e^{-}p$ running period.
% The contiued running of HERA until August 2007 and increase in integrated
% luminosity expected for the rest of the HERA-II programme  will
% hopefully allow us to have an improved look at events with isolated
% tau leptons.
% 
% %
%   References for Contact Interaction paper
%
\begin{thebibliography}{99}

% H1 tau paper
\bibitem{tauHERA1}
H1 Collaboration; {\it Tau Lepton Production in ep Collisions at HERA},
DESY-06-029, Apr 2006., Submitted to Eur.Phys.J.C, hep-ex/0604022

\bibitem{eps05Results}
H1 Collaboration; {\it Search for Events with Isolated Leptons and Missing Transverse Momentum at HERA},
contributed paper to {\it The International Europhysics Conference on High Energy Physics, EPS05}, Lisbon 2005, {\bf Abstract 637}.

% H1 IsoLep paper
\bibitem{isolAndreev2003} 
V.~Andreev {\em et al.} [H1 collaboration],
Phys. Lett. B~{\bf 561} (2003) 241 [hep-ex/0301030].


          
\end{thebibliography}

\renewcommand{\arraystretch}{1.5}
\begin{table}[hhh]
\begin{center}
\begin{tabular}{|l|r l|}
\hline
\multicolumn{3}{|c|}{\bf Selection of \boldmath{$\tau + P^{\rm miss}_T$} Events} \\
\hline \hline
\multirow{4}{20mm}{$P_T^\mathrm{miss}$ + Isolated Jet Preselection}& $P_T^\mathrm{calo}$ & $>\;\;$~$12$ GeV \\
 & $P_T^\mathrm{miss}$ & $>\;\;$~$12$ GeV \\
 & $E-P_z$ & $<\;\;$~$50$ GeV \\
 & $V_{ap}/V_{p}$ & $<\;\;0.5$ \;\;($<0.15 \;\mathrm{for}\; P_T^\mathrm{calo}<25$~GeV) \\
 & $N_{jets}$ & $>\;\;$~$1$ \\
 & $P^{jet}_T$ & $>\;\;$~$7$ GeV \\
 & $20^\circ$ & $<\;\;\theta_{jet}$~$\;\;<\; 120^\circ$ \\
 & $D_{track}$ & $>\;\; 1.0$  \\
 & $D_{jet}$ & $>\;\; 1.0$  \\
\hline
\multirow{5}{18mm}{Final $\tau+P_T^\mathrm{miss}$ Selection }& $N^{jet}_{tracks}$ & $ =\;\; 1$  \\
& $P_T^{track}$ & $>\;\; 5$ GeV \\
& $R_{jet}$             & $<\;\; 0.12$ \\
& $\Delta \phi$ & $< \;\;170^{\circ} $ \\
\hline
\end{tabular}
\caption{Selection criteria for events containing an isolated $\tau$ lepton and large $P^{\rm miss}_T$.}
\label{taucuts}
\end{center}
\end{table}

\clearpage
%\vspace{3cm}

% \renewcommand{\arraystretch}{1.5}
% \begin{table}[hhh]
% \begin{center}
% \begin{tabular}{|l|r l|}
% \hline
% \multicolumn{3}{|c|}{\bf Selection of \boldmath{$\tau + P^{\rm miss}_T$} events} \\
% \hline \hline
% %\multirow{4}{20mm}
% {CC-like Selection}& $P_T^\mathrm{miss}$ & $>$ 12 GeV \\
%  & $E-P_z$ & $<$ 50 GeV \\
%  & $\frac{Vap}{Vp}$ & $<0.5$ ($<0.15 \;\mathrm{for}\; P_T^{calo}<25$~GeV) \\ 
% \hline
% \hline
% %\multirow{3}{18mm}
% {$\tau$--jet} Candidate & $P^{\rm jet}_T$ & $>$ 7 GeV \\
%  & $20^\circ$ & $ < \theta^{\rm jet} < 120^{\,\circ}$ \\ 
%  & $R_{\rm jet}$             & $< 0.12$ \\
%  & $N^{\rm jet}_{tracks}$ & $ = 1$  \\
%  & $P_T^{track}$      & $> 5$ GeV \\
% \hline
% \hline
% Final Selection & $D_{{\rm jets},e,\mu}$    & $> 1.0$ \\
% & $\Delta \phi_{\tau - X}$ & $< 170^{\,\circ} $ \\ 
% & $D_{\rm tracks}$ & $> 1.0$ \\
% \hline
% \end{tabular}
% \caption{Selection criteria for isolated $\tau$ leptons in events 
% with large $P^{\rm miss}_T$. The description of {$\tau$--jet} Candidates as
% defined in the middle part of the table were also checked in samples
% of NC DIS ($E_e > 11\,\GeV$, $Q_e^2 > 100\,\GeV$) and Photoproduction 
% ($Q_e^2 < 1\,\GeV$, $V_{ap}/V_p > 0.15$). }
% \label{taucuts}
% \end{center}
% \end{table}

%\renewcommand{\arraystretch}{1.5}
%\begin{table}[hhh]
%\begin{center}
%\begin{tabular}{|l|r l|}
%\hline
%\multicolumn{3}{|c|}{\bf Selection of \boldmath{$\tau$}-jet candidates} \\
%\hline \hline
%%\multirow{3}{18mm}
%{$\tau$--jet} & $P^{jet}_T$ & $>$ 7 GeV \\
% & $20^\circ$ & $ < \theta^{jet} < 120^\circ$ \\ 
% & $R_{jet}$             & $< 0.12$ \\
% & $N^{jet}_{tracks}$ & $ = 1$  \\
%\hline
%\end{tabular}
%\caption{Selection criteria for $\tau$-jet candidates. $tau$-jet candidates
%are used in the selection of the final sample. Their description in CC DIS,
%NC DIS and photoproduction samples was checked to control the size of the
%SM background in the final sample.}
%\label{taujetcuts}
%\end{center}
%\end{table}


%\renewcommand{\arraystretch}{1.5}
%\begin{table}[hhh]
%\begin{center}
%\begin{tabular}{|l|r l|}
%\hline
%\multicolumn{3}{|c|}{\bf Selection of control samples} \\
%\hline \hline
%%\multirow{3}{18mm}
%NC DIS &         & $ \ge 1 $ isolated $ e^{\pm} $ \\
%       & $E_e$   & $> 11 \,\GeV$ \\
%       & $Q^2_e$ & $ > 100 \,\GeV$ \\ 
%\hline \hline
%Photoproduction & $Q^2_e$ & $ < 1 \,\GeV $ \\
%       & $V_{ap}/V_p$   & $> 0.15$ \\
%\hline
%\end{tabular}
%\caption{Selection criteria for the inclusive control samples. Description
%of $tau$-candidates was checked in these samples with and without PTmiss cut. }
%\label{controlsel}
%\end{center}
%\end{table}

\begin{table}
  \renewcommand{\arraystretch}{1.5} 
  \begin{center}

\input{TableCombined.tex}

\caption{Summary of the H1 search for events with tau leptons and missing 
        transverse momentum for the $e^{+}p$ data
	($\cal L$=153 pb$^{-1}$), $e^{-}p$ data ($\cal L$=125 pb$^{-1}$) and 
        the full HERA data set ($\cal L$=278 pb$^{-1}$).
        The results are shown for the full selected sample and for the 
        subsample at large $P_{T}^{X}>25$~GeV. 
        The number of observed events is compared to the SM prediction. The signal (W decay into $\tau$) 
        and the background contributions are also shown.
        The quoted errors contain statistical and systematic uncertainties 
        added in quadrature.}
  \end{center}
\end{table}


%\clearpage

\begin{figure}[ht] 
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-06-064.fig1.eps}
  \end{center}
  \caption{The hadronic transverse momentum distribution of 
    $\tau + P_T^{\rm miss}$ events in
    HERA $e^{+}p$ data (${\cal L}=153$~pb$^{-1}$) is compared to the SM
    expectation (open histogram).  The signal component of the SM
    expectation, dominated by real $W$ production, is given by the
    hatched histogram. $\rm N_{Data}$ is the total number of data
    events observed, $\rm N_{SM}$ is the total SM expectation. The
    total error on the SM expectation is given by the shaded band.}
  \label{fig:ptxheraposi}
\end{figure} 

\begin{figure}[ht] 
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-06-064.fig2.eps}
  \end{center}
  \caption{The hadronic transverse momentum distribution of 
    $\tau + P_T^{\rm miss}$ events in
    HERA $e^{-}p$ data (${\cal L}=125$~pb$^{-1}$) is compared to the SM
    expectation (open histogram).  The signal component of the SM
    expectation, dominated by real $W$ production, is given by the
    hatched histogram. $\rm N_{Data}$ is the total number of data
    events observed, $\rm N_{SM}$ is the total SM expectation. The
    total error on the SM expectation is given by the shaded band.}
  \label{fig:ptxheraelec}
\end{figure} 

\begin{figure}[ht] 
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-06-064.fig3.eps}
  \end{center}
  \caption{The hadronic transverse momentum distribution of 
    $\tau + P_T^{\rm miss}$ events in
    HERA $e^{\pm}p$ data (${\cal L}=278$~pb$^{-1}$) is compared to the SM
    expectation (open histogram).  The signal component of the SM
    expectation, dominated by real $W$ production, is given by the
    hatched histogram. $\rm N_{Data}$ is the total number of data
    events observed, $\rm N_{SM}$ is the total SM expectation. The
    total error on the SM expectation is given by the shaded band.}
  \label{fig:ptxheraall}
\end{figure} 

\begin{figure}[htp] 
  \begin{center}
\epsfig{file = H1prelim-06-064.fig4.eps, width=17cm }
  \end{center}
  \caption{Candidate event with an isolated tau and $P_T^\mathrm{miss}$ containing a prominent \newline hadronic system $X$.}
  \label{fig:taucand1}
\end{figure} 

\begin{figure}[ht] 
  \begin{center}
\epsfig{file =H1prelim-06-064.fig5.eps, width=17cm }
  \end{center}
  \caption{Candidate event with isolated tau and $P_T^\mathrm{miss}$ containing a prominent \newline hadronic system $X$.}
  \label{fig:taucand2}
\end{figure} 

\begin{figure}[ht] 
  \begin{center}
\epsfig{file =H1prelim-06-064.fig6.eps, width=17cm }
  \end{center}
  \caption{Candidate event with isolated tau and $P_T^\mathrm{miss}$ containing a prominent \newline hadronic system $X$.}
  \label{fig:taucand3}
\end{figure} 

\end{document}

