\relax 
\citation{Ahmed:1994aw,Adloff:1998aw,Breitweg:1998aw,Andreev:2003pm}
\citation{Aktas:2003yd,zeus_singletop}
\citation{tauzeus}
\citation{EPVEC}
\citation{SPIRA}
\citation{PRIVSPI}
\citation{GRAPE}
\@writefile{toc}{\contentsline {section}{\numberline {1}Introduction}{1}}
\@writefile{toc}{\contentsline {section}{\numberline {2}Processes and their Monte Carlo Simulation}{1}}
\citation{DJANGO}
\citation{RAPGAP}
\citation{PYTHIA}
\citation{JETSET74}
\citation{SFGRVGLO}
\citation{Aktas:2003yd}
\citation{Brun:1987ma}
\citation{H1detector}
\@writefile{toc}{\contentsline {section}{\numberline {3}Experimental Conditions}{2}}
\citation{h1cal}
\citation{h1testbeam}
\citation{h1spacal}
\citation{h1plug}
\@writefile{toc}{\contentsline {section}{\numberline {4}Search for Events with Missing Transverse Momentum and Isolated Tau Leptons}{3}}
\bibcite{Ahmed:1994aw}{1}
\bibcite{Adloff:1998aw}{2}
\bibcite{Breitweg:1998aw}{3}
\bibcite{Andreev:2003pm}{4}
\bibcite{zeus_singletop}{5}
\bibcite{Aktas:2003yd}{6}
\bibcite{tauzeus}{7}
\bibcite{EPVEC}{8}
\@writefile{toc}{\contentsline {section}{\numberline {5}Observation of Tau Pairs in Elastic $\gamma \gamma $--processes.}{6}}
\@writefile{toc}{\contentsline {section}{\numberline {6}Conclusions}{6}}
\bibcite{SPIRA}{9}
\bibcite{PRIVSPI}{10}
\bibcite{GRAPE}{11}
\bibcite{DJANGO}{12}
\bibcite{RAPGAP}{13}
\bibcite{PYTHIA}{14}
\bibcite{JETSET74}{15}
\bibcite{SFGRVGLO}{16}
\bibcite{Brun:1987ma}{17}
\bibcite{H1detector}{18}
\bibcite{h1cal}{19}
\bibcite{h1testbeam}{20}
\bibcite{h1spacal}{21}
\bibcite{h1plug}{22}
\@writefile{lot}{\contentsline {table}{\numberline {1}{\ignorespaces The preselection of events with missing transverse momentum: $P_T^{calo}$ is the total calorimetric transverse momentum, $P_T^{miss}$ is the total transverse momentum of all reconstructed particles, $\Delta \phi \left ( Calo, \unhbox \voidb@x \hbox {PLUG} \right )$ is the acoplanarity between the momentum measured in the main calorimeter and the momentum measured in the forward PLUG calorimeter, $\Sigma (E-P_z)$ sums the $E-P_z$ contributions of all measured particles and is 55.2GeV for events with fully measured final state. At least one jet is required with a transverse momentum above 7 GeV. }}{8}}
\newlabel{cuts1}{{1}{8}}
\@writefile{lot}{\contentsline {table}{\numberline {2}{\ignorespaces  The preselection of events with significant missing transverse momentum and a single track jet, corresponding to a tau candidate. The jet polar angle $\theta ^{jet}$ is required to be in the central region and to contain exactly one charged track with a transverse momentum above 2\nobreakspace  {}GeV. The jet is required to be isolated by asking the minimum distance in the $\eta -\varphi $ plane to or other tracks or jets in the event to be above 1. }}{8}}
\newlabel{cuts2}{{2}{8}}
\@writefile{lot}{\contentsline {table}{\numberline {3}{\ignorespaces Final selection of events with isolated tau candidates and missing transverse momentum. Narrow calorimetric deposits are identified using the variable $R^{jet}$ (jet size), defined by $ R_{jet} = \DOTSB \sum@ \slimits@ _i \frac  {E_i \Delta ^i(\varphi ,\eta )}{E^{jet}}$ ( $i$ runs over all particles in the jet, $E_i$ is the particle energy and $\Delta ^i(\varphi ,\eta )$ the distance in $\eta -\varphi $ plane to the jet axis). The hadronic final state excluding the tau candidate jet is denoted by $X$. A significant acoplanarity requirement $\Delta \phi (jet,X)< 170^{\circ }$ ensures further background rejection. }}{9}}
\newlabel{cuts3}{{3}{9}}
\@writefile{lot}{\contentsline {table}{\numberline {4}{\ignorespaces Observed and predicted number of events in the 1996-2000 dataset after the final selection. Also shown is the the product of the efficiency and the branching fraction for the anomalous single top production detected in the channel $t\rightarrow b W (\rightarrow \tau \nu _\tau )$ (the present analysis is only sensitive to the one-prong hadronic tau decays)}}{9}}
\newlabel{results}{{4}{9}}
\@writefile{lof}{\contentsline {figure}{\numberline {1}{\ignorespaces The distributions of $\Sigma (E - P_z)$, $P_T^{calo}$ and the highest $P_T^{jet}$ in the data compared to the Monte Carlo simulation for the $P_T^{miss}$ event preselection described in table 1\hbox {}. The SM $W$ contribution is still negligible at this level.}}{10}}
\newlabel{step1a}{{1}{10}}
\@writefile{lof}{\contentsline {figure}{\numberline {2}{\ignorespaces The distributions of $R^{jet}$ and $P_T^X$ in the data compared with the Monte Carlo simulation for the $P_T^{miss}$ event preselection described in table 1\hbox {}. The SM $W$ contribution is still negligible at this level.}}{11}}
\newlabel{step1b}{{2}{11}}
\@writefile{lof}{\contentsline {figure}{\numberline {3}{\ignorespaces The distributions of $R^{jet}$ and $P_T^X$ in the data compared with the Monte Carlo simulation for the $\tau +P_T^{miss}$ event preselection described in table 2\hbox {}. Note that the jet radius $R^{jet}$ of jets selected in the Standard Model $W$ Monte Carlo are narrow, as expected from tau jets. A cut $R^{jet} < 0.12$ is applied later in the final selection.}}{11}}
\newlabel{step2}{{3}{11}}
\@writefile{lof}{\contentsline {figure}{\numberline {4}{\ignorespaces  The distribution of the hadronic transverse momentum $P_T^X$ in the data compared with the Monte Carlo simulation for the $\tau +P_T^{miss}$ final selection described in table 3\hbox {}. No events are observed in the high $P_T^X$ region, where events for the template signal process sing-le $top$ production are expected.}}{12}}
\newlabel{ptxfinal}{{4}{12}}
\@writefile{lot}{\contentsline {table}{\numberline {5}{\ignorespaces Summary of the results of searches for events with isolated leptons, missing transverse momentum and large $P_T^{X}$ at HERA. The number of observed events is compared to the SM prediction. The $W^\pm $ component is given in parentheses in percent. The statistical and systematic uncertainties added in quadrature are also indicated.}}{12}}
\newlabel{heraisolep}{{5}{12}}
\@writefile{lof}{\contentsline {figure}{\numberline {5}{\ignorespaces Control Plots of the visible transverse momentum distributions of the hadronically decaying tau lepton; on the left for opposite charges of the two decaying tau candidates, on the right for equally charged tau candidates. In $\gamma \gamma \rightarrow \tau ^{+} \tau ^{-}$ processes only candidates of opposite charge are expected.}}{13}}
\newlabel{taupairpt}{{5}{13}}
\@writefile{lof}{\contentsline {figure}{\numberline {6}{\ignorespaces  Tau--pair candidate event with one tau lepton decaying leptonically to a muon, and the other tau lepton decaying to three charged hadrons (3-prong topology). The scattered positron is also detected in the backward calorimeter.}}{14}}
\newlabel{event}{{6}{14}}