%================================================================ % LaTeX file with preferred layout for the contributed papers to % the DIS 2006 % % process with: latex hep98.tex % dvips -D600 hep98 %================================================================ \documentclass[12pt]{article} \usepackage{epsfig} \usepackage{amsmath} \usepackage{hhline} \usepackage{amssymb} \usepackage{times} \usepackage{multirow} \renewcommand{\topfraction}{1.0} \renewcommand{\bottomfraction}{1.0} \renewcommand{\textfraction}{0.0} \newlength{\dinwidth} \newlength{\dinmargin} \setlength{\dinwidth}{21.0cm} \textheight23.5cm \textwidth16.0cm \setlength{\dinmargin}{\dinwidth} \setlength{\unitlength}{1mm} \addtolength{\dinmargin}{-\textwidth} \setlength{\dinmargin}{0.5\dinmargin} \oddsidemargin -1.0in \addtolength{\oddsidemargin}{\dinmargin} \setlength{\evensidemargin}{\oddsidemargin} \setlength{\marginparwidth}{0.9\dinmargin} \marginparsep 8pt \marginparpush 5pt \topmargin -42pt \headheight 12pt \headsep 30pt \footskip 24pt \parskip 3mm plus 2mm minus 2mm %===============================title page============================= % Some useful tex commands % \newcommand{\GeV}{\rm GeV} \newcommand{\TeV}{\rm TeV} \newcommand{\pb}{\rm pb} \newcommand{\cm}{\rm cm} \newcommand{\hdick}{\noalign{\hrule height1.4pt}} \begin{document} \pagestyle{empty} \begin{titlepage} \noindent \begin{center} %{\it {\large version of \today}} \\[.3em] \begin{small} \begin{tabular}{llrr} %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 Submitted to & & & %\epsfig{file=H1logo_bw_small.epsi,width=2.cm} \epsfig{file=/h1/www/images/H1logo_bw_small.epsi ,width=2.cm} \\[.2em] \hline \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] \end{tabular} \end{small} \end{center} \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}