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\begin{titlepage}

\vspace{1cm}

\begin{flushright}
April, 2007
\end{flushright}

\vspace{4cm}

\begin{center}

\begin{Large}

{\bf \boldmath Search for Events with Isolated Leptons and Missing Transverse Momentum: Update}

\vspace{2cm}

H1 Collaboration

\end{Large}
\end{center}

\noindent

This document presents an update of the previous preliminary results in the search for
events with isolated leptons (electrons or muons) and missing transverse momentum in $e^\pm p$
collisions with the H1 detector at HERA in the period 1994--2006 \cite{ichep06Results}.
The analysis now examines the complete H1 data sample, corresponding to an integrated luminosity
of 478~pb$^{-1}$, which includes 189~pb$^{-1}$ of $e^{+}p$ data (2003-04 and 2006-07) and
170~pb$^{-1}$ of $e^{-}p$ data (2004-06) from the HERA~II phase. A total of 59 events are observed
in the data, compared to a Standard Model (SM) prediction of 58.9~$\pm$~8.1.

At large hadronic transverse momentum $P_{T}^{X} >$ 25 GeV, a total of 24 events are
observed compared to a SM prediction of 15.8~$\pm$~2.5. In this region, 21 events are
observed in the $e^{+}p$ data compared to a SM prediction of 8.9~$\pm$~1.5, whereas in
the $e^{-}p$ data 3 events are observed compared to a SM prediction of 6.9~$\pm$~1.0.
Events with large transverse momentum are observed in both the HERA I and II $e^{+}p$ samples.
Further details of the analysis may be found in \cite{isolAndreev2003}.

A comparison of the efficiency of the H1 and ZEUS experiments to detect events
containing isolated electrons or muons and missing transverse momentum is also presented.

\end{titlepage}

\newpage

\pagestyle{plain}

\begin{figure}[p] 
  \begin{center}
      \includegraphics[width=16cm]{H1prelim-07-063.fig1.eps}
  \end{center}
\begin{picture} (0.,0.)
\setlength{\unitlength}{1.0cm}
\put (0.2,9.05){\bf\Large Event with $e^{+}+P_T^{\rm miss}$ in the HERA II $e^{+}p$ data }
\put (0.2,8.05){\bf\large $\mathbf P_T^e=47$~GeV, $\mathbf P_T^{\rm miss}=47$~GeV}
\put (10.22,2.75){\bf\Large $e^+$} 
\end{picture}
\caption{Display of an event with an isolated electron and missing transverse momentum:
	a candidate for elastic $W$ production in the HERA II $e^{+}p$ data.}
\label{fig:electronone}
\end{figure} 
%
%
%
%
\begin{figure}[p] 
  \begin{center}
      \includegraphics[width=16cm]{H1prelim-07-063.fig2.eps}
  \end{center}
\begin{picture} (0.,0.)
\setlength{\unitlength}{1.0cm}
\put (0.2,9.05){\bf\Large Event with $e^{+}+P_T^{\rm miss}$ in the HERA II $e^{+}p$ data }
\put (0.2,8.05){\bf\large $\mathbf P_T^e=37$~GeV, $\mathbf P_T^{\rm miss}=44$~GeV, $\mathbf P_T^{X}=29$~GeV}
\put (10.66,2.45){\bf\Large $e^+$} 
\put (14.04,3.40){\bf\Large $X$} 
\end{picture}
\caption{Display of an event with an isolated electron, missing transverse momentum
	and a prominent hadronic jet in the HERA II $e^{+}p$ data.}
\label{fig:electrontwo}
\end{figure} 

\clearpage

\begin{figure}[t] 
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-07-063.fig3.eps}
  \end{center}
\begin{picture} (0.,0.)
\setlength{\unitlength}{1.0cm}
\put (0.2,9.05){\bf\Large Event with $\mu^{-}+P_T^{\rm miss}$ in the HERA II $e^{-}p$ data }
\put (0.2,8.05){\bf\large $\mathbf P_T^\mu=38$~GeV, $\mathbf P_T^{\rm miss}=51$~GeV,
	$\mathbf P_T^{X}=24.7$~GeV}
\put (13.3,4.4){\bf\Large $X$}
\put (12.0,6.95){\bf\Large $\mu^{-}$}
\end{picture}
\caption{Display of an event with an isolated muon, missing transverse
	momentum and a prominent hadronic jet in the HERA II $e^{-}p$ data.}
\label{fig:muonone}
\end{figure} 
%
%
%
%
\begin{figure}[t] 
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-07-063.fig4.eps}
  \end{center}
\begin{picture} (0.,0.)
\setlength{\unitlength}{1.0cm}
\put (0.2,9.05){\bf\Large Event with $\mu^{-}+P_T^{\rm miss}$ in the HERA II $e^{+}p$ data }
\put (0.2,8.05){\bf\large $\mathbf P_T^\mu=51$~GeV, $\mathbf P_T^{\rm miss}=39$~GeV,
	$\mathbf P_T^{X}=48$~GeV}
\put (12.3,6.1){\bf\Large $X$}
\put (11.85,2.15){\bf\Large $\mu^{-}$}
\end{picture}
\caption{Display of an event with an isolated muon, missing transverse
	momentum and a prominent hadronic jet in the HERA II $e^{+}p$ data.}
\label{fig:muontwo}
\end{figure} 

\clearpage

\begin{table}%%%%%[htb]
  \renewcommand{\arraystretch}{2.1}
  \begin{center}
    \begin{tabular}{|r||c|c||c|} 
    \multicolumn{4}{c}{\Large H1 Preliminary, HERA II e$^{+}$p (189~pb$^{-1}$)}\\
    \hline
    { \large Electron          }&{H1 Data }&{SM Expectation  }&{SM Signal} \\
    \hline
    \hline  
    { \large Full Sample       }&{16}      &{17.5 $\pm$ 2.5}&{12.3 $\pm$ 2.0} \\
    \hline  
    { \large $P_{T}^{X}>$25 GeV}&{ 7}      &{ 3.2 $\pm$ 0.6}&{ 2.3 $\pm$ 0.4} \\
    \hline \hline      
    { \large Muon              }&{ H1 Data}&{SM Expectation  }&{SM Signal} \\
    \hline
    \hline  
    { \large Full Sample       }&{ 7}      &{ 4.6 $\pm$ 0.7}&{ 3.9 $\pm$ 0.6} \\
    \hline  
    { \large $P_{T}^{X}>$25 GeV}&{ 4}      &{ 2.8 $\pm$ 0.4}&{ 2.3 $\pm$ 0.4} \\
    \hline \hline
    { \large Combined          }&{H1 Data }&{SM Expectation  }&{SM Signal} \\
    \hline
    \hline  
    { \large Full Sample       }&{23}      &{22.1 $\pm$ 3.1}&{16.2 $\pm$ 2.6} \\
    \hline  
    { \large $P_{T}^{X}>$25 GeV}&{11}      &{ 6.0 $\pm$ 1.0}&{ 4.6 $\pm$ 0.7} \\
    \hline
  \end{tabular}
  \caption{The results of the search for events with isolated electrons or muons and missing
	transverse momentum in the HERA II $e^{+}p$ data (189~pb$^{-1}$): observed
	and predicted numbers of events in the electron channel, the muon channel and the
	sum of electron and muon channels. The signal component of the SM expectation, dominated
	by real $W$ production, is also given. The quoted errors contain statistical and
	systematic uncertainties added in quadrature.}
  \end{center}
\label{tab:heraIIeplus}
\end{table}

\clearpage

\begin{table}
  \renewcommand{\arraystretch}{2.1}
  \begin{center}
    \begin{tabular}{|r||c|c||c|} 
    \multicolumn{4}{c}{\Large H1 Preliminary, HERA II e$^{-}$p (170~pb$^{-1}$)}\\
    \hline
    { \large Electron          }&{H1 Data }&{SM Expectation  }&{SM Signal} \\
    \hline
    \hline  
    { \large Full Sample       }&{15}      &{17.7 $\pm$ 2.5}&{11.7 $\pm$ 1.9} \\
    \hline  
    { \large $P_{T}^{X}>$25 GeV}&{ 2}      &{ 3.5 $\pm$ 0.6}&{ 2.1 $\pm$ 0.4} \\
    \hline \hline     
    { \large Muon              }&{ H1 Data}&{SM Expectation  }&{SM Signal} \\
    \hline
    \hline  
    { \large Full Sample       }&{ 2}      &{ 4.7 $\pm$ 0.7}&{ 3.7 $\pm$ 0.6} \\
    \hline  
    { \large $P_{T}^{X}>$25 GeV}&{ 0}      &{ 2.9 $\pm$ 0.4}&{ 2.1 $\pm$ 0.4} \\
    \hline \hline
    { \large Combined          }&{H1 Data }&{SM Expectation  }&{SM Signal} \\
    \hline
    \hline  
    { \large Full Sample       }&{17}      &{22.4 $\pm$ 3.1}&{15.3 $\pm$ 2.4} \\
    \hline  
    { \large $P_{T}^{X}>$25 GeV}&{ 2}      &{ 6.4 $\pm$ 1.0}&{ 4.2 $\pm$ 0.7} \\
    \hline
  \end{tabular}
  \caption{The results of the search for events with isolated electrons or muons and missing
	transverse momentum in the HERA II $e^{-}p$ data (170~pb$^{-1}$): observed
	and predicted numbers of events in the electron channel, the muon channel and the
	sum of electron and muon channels. The signal component of the SM expectation, dominated
	by real $W$ production, is also given. The quoted errors contain statistical and
	systematic uncertainties added in quadrature.}
  \end{center}
\label{tab:heraIIminus}
\end{table}

\clearpage

\begin{table}
 \renewcommand{\arraystretch}{1.6}
\begin{center}
  \begin{tabular}{|c|c|c|c|c|}
    \hline
    \multicolumn{2}{|c|}{\large H1 Preliminary} &
    Electron &
    Muon &
    Combined \\
    \multicolumn{2}{|c|}{$l$+$P_{T}^{\rm miss}$ events at} &
    obs./exp. &
    obs./exp. &
    obs./exp. \\
    \multicolumn{2}{|c|}{HERA I+II} &
    {\footnotesize (Signal contribution)} &
    {\footnotesize (Signal contribution)} &
    {\footnotesize (Signal contribution)} \\
    \hline
    \hline
    {\footnotesize $e^{+} p$} &
    {\footnotesize Full Sample} &
    {\footnotesize 26 / 27.3 $\pm$ 3.8 (71\%)}&
    {\footnotesize 15 /  7.2 $\pm$ 1.1 (85\%)}&
    {\footnotesize 41 / 34.5 $\pm$ 4.8 (74\%)}\\
    \cline{2-5}
    {\footnotesize 294 pb$^{-1}$} &
    {\footnotesize $P_{T}^{X}~>25$~GeV} &
    {\footnotesize 11 /  4.7 $\pm$ 0.9 (75\%)}&
    {\footnotesize 10 /  4.2 $\pm$ 0.7 (85\%)}& 
    {\footnotesize 21 /  8.9 $\pm$ 1.5 (80\%)}\\
    \hline
    \hline
    {\footnotesize $e^{-} p$} &
    {\footnotesize Full Sample} &
    {\footnotesize 16 / 19.4 $\pm$ 2.7 (65\%)}&
    {\footnotesize  2 /  5.1 $\pm$ 0.7 (78\%)}&
    {\footnotesize 18 / 24.4 $\pm$ 3.4 (68\%)}\\
    \cline{2-5}
    {\footnotesize 184 pb$^{-1}$} &
    {\footnotesize $P_{T}^{X}~>25$~GeV} &
    {\footnotesize  3 /  3.8 $\pm$ 0.6 (61\%)}&
    {\footnotesize  0 /  3.1 $\pm$ 0.5 (74\%)}& 
    {\footnotesize  3 /  6.9 $\pm$ 1.0 (67\%)}\\
    \hline
    \hline
    {\footnotesize $e^{\pm} p$} &
    {\footnotesize Full Sample} &
    {\footnotesize 42 / 46.7 $\pm$ 6.5 (69\%)}&
    {\footnotesize 17 / 12.2 $\pm$ 1.8 (82\%)}&
    {\footnotesize 59 / 58.9 $\pm$ 8.2 (72\%)}\\
    \cline{2-5}
    {\footnotesize 478 pb$^{-1}$} &
    {\footnotesize $P_{T}^{X}~>25$~GeV} &
    {\footnotesize 14 /  8.5 $\pm$ 1.5 (68\%)}&
    {\footnotesize 10 /  7.3 $\pm$ 1.2 (79\%)}& 
    {\footnotesize 24 / 15.8 $\pm$ 2.5 (73\%)}\\
    \hline
  \end{tabular}
  \caption{Summary of the H1 results of searches for events with isolated electrons or muons and
	missing transverse momentum for the $e^{+}p$ data (294~pb$^{-1}$), $e^{-}p$ data
	(184~pb$^{-1}$) and the full HERA I+II data set (478~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 component of the
	SM expectation, dominated by real $W$ production, is given as a percentage in parentheses.
        The quoted errors contain statistical and systematic uncertainties added in quadrature.}
\end{center}
\label{tab:summary}
\end{table}

\clearpage

\begin{figure}
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-07-063.fig5.eps}
  \end{center}
  \caption{The hadronic transverse momentum distribution in the electron and muon channels combined:
    data (HERA I+II $e^{+}p$, 294~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:ptxhera_e+}
\end{figure} 

\clearpage

\begin{figure}
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-07-063.fig6.eps}
  \end{center}
  \caption{The hadronic transverse momentum distribution in the electron and muon channels combined:
    data (HERA I+II $e^{-}p$, 184~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:ptxhera_e-}
\end{figure} 

\clearpage

\begin{figure}
  \begin{center}
      \includegraphics[width=15cm]{H1prelim-07-063.fig7.eps}
  \end{center}
  \caption{The hadronic transverse momentum distribution in the electron and muon channels combined:
    data (HERA I+II $e^{\pm}p$, 478~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:ptxhera_e+e-}
\end{figure}

\clearpage

\begin{figure}
  \begin{center}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig8a.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig8b.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig8c.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig8d.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (6.0,9.4){\bf\Large a)}
    \put (14.0,9.4){\bf\Large b)}
    \put (6.0,2.3){\bf\Large c)}
    \put (14.0,2.3){\bf\Large d)}
  \end{picture}
\caption{Comparisons of the efficiencies of the H1 and ZEUS analyses to select
	events containing isolated electrons or muons and missing transverse
	momentum in the HERA $e^{+}p$ data. Figure a) displays the efficiency,
	defined as $N_{rec}$~/~$N_{gen}$, as function of hadronic transverse momentum
	$P_{T}^{X}$ in the electron channel. Figure b) displays the efficiency in
	the electron channel at large $P_{T}^{X} >$~25~GeV as a function of
	electron polar angle. Figure c) displays the efficiency as function of
	hadronic transverse momentum $P_{T}^{X}$ in the muon channel. Figure d)
	displays the efficiency in the muon channel at large $P_{T}^{X} >$~25~GeV
	as a function of muon polar angle. In all figures the H1 (ZEUS) efficiency
	is given by the solid (dashed) line. The data events observed by each
	experiment are indicated by the arrows. The $\theta_{l}$ distribution
	from EPVEC is also shown in figures b) and d).}
\label{fig:h1-zeusHERAe+}
\end{figure}

\clearpage

\begin{figure}
  \begin{center}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig9a.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig9b.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig9c.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig9d.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (6.0,9.4){\bf\Large a)}
    \put (14.0,9.4){\bf\Large b)}
    \put (6.0,2.3){\bf\Large c)}
    \put (14.0,2.3){\bf\Large d)}
  \end{picture}
\caption{Comparisons of the efficiencies of the H1 and ZEUS analyses to select
	events containing isolated electrons or muons and missing transverse
	momentum in the HERA $e^{-}p$ data. Figure a) displays the efficiency,
	defined as $N_{rec}$~/~$N_{gen}$, as function of hadronic transverse momentum
	$P_{T}^{X}$ in the electron channel. Figure b) displays the efficiency in
	the electron channel at large $P_{T}^{X} >$~25~GeV as a function of
	electron polar angle. Figure c) displays the efficiency as function of
	hadronic transverse momentum $P_{T}^{X}$ in the muon channel. Figure d)
	displays the efficiency in the muon channel at large $P_{T}^{X} >$~25~GeV
	as a function of muon polar angle. In all figures the H1 (ZEUS) efficiency
	is given by the solid (dashed) line. The data events observed by each
	experiment are indicated by the arrows. The $\theta_{l}$ distribution
	from EPVEC is also shown in figures b) and d).}
\label{fig:h1-zeusHERAe-}
\end{figure}

\clearpage

\begin{figure}
  \begin{center}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig10a.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig10b.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig10c.eps}
    \includegraphics[width=.49\textwidth]{H1prelim-07-063.fig10d.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (6.0,9.4){\bf\Large a)}
    \put (14.0,9.4){\bf\Large b)}
    \put (6.0,2.3){\bf\Large c)}
    \put (14.0,2.3){\bf\Large d)}
  \end{picture}
\caption{Comparisons of the efficiencies of the H1 and ZEUS analyses to select
	events containing isolated electrons or muons and missing transverse
	momentum in the HERA $e^{\pm}p$ data. Figure a) displays the efficiency,
	defined as $N_{rec}$~/~$N_{gen}$, as function of hadronic transverse momentum
	$P_{T}^{X}$ in the electron channel. Figure b) displays the efficiency in
	the electron channel at large $P_{T}^{X} >$~25~GeV as a function of
	electron polar angle. Figure c) displays the efficiency as function of
	hadronic transverse momentum $P_{T}^{X}$ in the muon channel. Figure d)
	displays the efficiency in the muon channel at large $P_{T}^{X} >$~25~GeV
	as a function of muon polar angle. In all figures the H1 (ZEUS) efficiency
	is given by the solid (dashed) line. The data events observed by each
	experiment are indicated by the arrows. The $\theta_{l}$ distribution
	from EPVEC is also shown in figures b) and d).}
\label{fig:h1-zeusHERAe+e-}
\end{figure}

\clearpage

\begin{thebibliography}{99}

\bibitem{ichep06Results}
H1 Collaboration; {\it ``Search for Events with Isolated Leptons and Missing Transverse Momentum at HERA''},
contributed paper to {\it The XXXIII International Conference on High Energy Physics, ICHEP06}, Moscow 2006.

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

\end{thebibliography}



\end{document}
