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                LP 2007}} \\
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    www-h1.desy.de/h1/www/publications}} \\[.2em]
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\begin{center}
  \Large
  {\bf Search for Leptoquark Bosons in {\boldmath{$ep$}} Collisions at HERA}

  \vspace*{1cm}
    {\Large H1 Collaboration} 
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% \begin{abstract}
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% A search for scalar and vector leptoquarks coupling to first generation fermions using the electron-- and positron--proton scattering data collected by the H1 experiment in the period 1994-2007 is presented. The data correspond to a total integrated luminosity of $92$\,pb$^{-1}$. 
% %Especially the sensitivity to leptoquarks with fermion number F=2 is increased w.r.t. the previous H1 results. 
% No evidence for the direct or indirect production of such particles is found in data samples with a large transverse momentum final state electron or with large missing transverse momentum. The results of the present analysis are used to set new constraints on leptoquark couplings. For leptoquark couplings of electromagnetic strength, F=2 leptoquarks with masses up to $276-304\,{\rm GeV}$ are ruled out.
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% Version 0.1 \today \\
% Editors: J.~List (jenny.list@desy.de), C.~Helebrant (Christian.Helebrant@desy.de)\\
% Referees: J.~Meyer (joachim.meyer@desy.de), S.~Schmitt (Stefan.Schmitt@desy.de)\\
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%   \Large
%   {\bf 
%    Search for Leptoquark Bosons in polarised {\boldmath{$e^-p$}} Collisions at HERA}
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%     {\Large H1 Collaboration} 
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\begin{abstract}
\noindent
A search for scalar and vector leptoquarks coupling to
first generation fermions is performed 
using the the full $e^+p$ and $e^-p$ scattering data collected by the H1 experiment
between 1994 and 2007. 
The data correspond to a total integrated luminosity of $449$\,pb$^{-1}$.
No evidence for direct or indirect production of such
particles is found in data samples with a large transverse
momentum final state electron or with large missing transverse
momentum.
For each of the leptoquark species defined in the Buchm\"uller, R\"uckl and Wyler model, the present analysis excludes a previosly unexplored domain in the plane spanned by the mass of the leptoquark and its coupling to fermions.  
%For
%leptoquark couplings of electromagnetic strength,
%leptoquarks with masses up to $275-325\,{\rm GeV}$ are ruled out.
%These limits improve and supercede earlier H1 limits based on 
% subsamples of the data used here.
%The exclusion limits also apply to squarks predicted by 
%supersymmetry scenarios with $R$-parity violation.

\noindent
\end{abstract}
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% (To be submitted to Phys.\ Lett.\ B)
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\section*{Introduction}

The $ep$ collider HERA offers the unique possibility to search for the 
resonant production of new particles coupling directly to a lepton and a parton. Leptoquarks (LQs), colour triplet bosons, which appear naturally in various unifying theories beyond the Standard Model (SM) 
are such an example. At HERA, leptoquarks could be singly produced by the fusion of the initial state lepton of energy $27.6 \GeV$ with a quark from the incoming proton of energy up to $920 \GeV$.

The phenomenology of LQs at HERA is discussed in detail in~\cite{H1LQHERA1}. The effective Lagrangian considered therein conserves lepton and baryon number, obeys the symmetries of the SM gauge groups $U(1)_Y$, $SU(2)_L$ and $SU(3)_C$ and includes both scalar and vector LQs. A dimensionless coupling $\lambda$ defines the coupling at the $e$-$q$-LQ vertex. At HERA, LQs can be resonantly produced in
the $s$-channel or exchanged in the $u$-channel between the incoming lepton and a quark coming from the proton. In the $s$-channel, a LQ is produced at a mass $M =\sqrt{s_{ep} x}$ where $x$ is the momentum fraction of the proton carried by the interacting quark.


\begin{table*}[htb]
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\begin{center}
    \begin{tabular}{lllll}
    Period & Collisions  & $\sqrt{s}$ &  E-beam polarisation  & Luminosity \\ \hline
    \multirow{3}{18mm}{HERA I}  & $e^+p$ & 301~GeV  & 0 & 37~pb$^{-1}$ \\ 
            & $e^-p$ & 319~GeV  & 0 & 14~pb$^{-1}$ \\ 
            & $e^+p$ & 319~GeV  & 0 & 64~pb$^{-1}$ \\ \hline
    \multirow{4}{18mm}{HERA II }  & $e^+p$ & 319~GeV  & +0.31 & 99~pb$^{-1}$ \\
            & $e^+p$ & 319~GeV  & -0.36 & 78~pb$^{-1}$ \\ 
            & $e^-p$ & 319~GeV  & -0.26 & 104~pb$^{-1}$ \\ 
            & $e^-p$ (NC) & 319~GeV  & +0.32 & 51~pb$^{-1}$ \\
            & $e^-p$ (CC) & 319~GeV  & +0.37 & 30~pb$^{-1}$ \\ \hline
	        \end{tabular}
\end{center}
\caption{The data sets used in the present search for leptoquarks. The present paper presents the analysis of the full HERA II data sets. The HERA I data samples are used as analysed in~\cite{H1LQHERA1}. }
\label{tab:datasets}
\end{table*}

Due to the more favourable quark-densities of quarks with respect to
anti-quarks at high $x$, the $e^{-}p$ data sets are mostly sensitive to LQs with fermion number\footnote{The fermion number $F$ is given by $F=|3B+L|$ with $B$ and $L$ being the baryon and lepton number respectively.} $F=2$, whereas $e^{+}p$ collisions are more favourable for the production of   $F=2$ LQs. The search reported here considers the decays  ${\rm{LQ}} \rightarrow eq$ and ${\rm{LQ}} \rightarrow \nu q$ where $q$ represents both quarks and anti-quarks. Such LQ decays lead to final states similar to those of deep-inelastic scattering (DIS) neutral current (NC) and charged current (CC) interactions at very high $Q^2$,
the negative four-momentum transfer squared. If the final state is of type $eq$, the LQ mass is reconstructed from the measured kinematics of the scattered  electron. If the final state is of type $\nu q$, the LQ mass is reconstructed from the hadronic final state~\cite{H1LQHERA1}.

This note presents a search for LQs coupling to first generation fermions with fermion number $F=0$ and $F=2$ in scattering of longitudinally polarised electrons or positron on protons at a centre-of-mass energy of $\sqrt{s_{ep}}$ of up to $\approx 320 \GeV$. The new HERA II data sets are analysed in the present preliminary analysis. The results of these searches are combined with the published results of LQ searches using HERA I data. The data samples\footnote{A small subsample of data corresponding to a part of the right-handed $e^-p$  run at HERA II is not used in the present preliminary CC analysis.} are summarised in table~\ref{tab:datasets}.


\section*{Neutral and Charged Current Event Selection}

The H1 detector components most relevant to this analysis are the liquid argon calorimeter, which measures the positions and energies of charged and neutral particles over the range  $4^\circ<\theta<154^\circ$ of polar angle\footnote{The polar angle $\theta$ is defined with respect to the incident proton momentum vector (the positive $z$ axis).}, and the inner tracking detectors which measure the angles and momenta of charged particles over the range $7^\circ<\theta<165^\circ$. A full description of the detector can be found in~\cite{h1det}. 

This search is based on inclusive NC and CC DIS event samples and follows closely the selection and kinematics reconstruction presented in~\cite{H1LQHERA1}.
% in the kinematic domain $Q^2>500\,\mathrm{GeV}^2$ and $0.1<y<0.9$, where the inelasticity variable $y$ is defined as $y=Q^2/M^2$. The cuts on $y$ remove regions of poor reconstruction, poor resolution, large QED radiative effects and background from photoproduction processes. 

The selection of NC DIS events %follows that presented in~\cite{H1LQ99}.
requires an identified electron with an energy above $11 \GeV$. The photon virtuality $Q^2$ and the event inelasticity $y$ are restricted to the ranges $Q^2>500\,\mathrm{GeV}^2$ and $0.1<y<0.9$, respectively.  Furthermore, a limited reconstructed momentum loss in direction of the incident electron is expected for the signal events, such that $40\GeV<E-P_z<70\GeV$ is demanded.  


The selection of CC DIS events 
%follows closely that presented in~\cite{H1LQHERA1}.
%A missing transverse momentum exceeding $25 \GeV$ is required.
%For the selection of CC-like events 
requires a significant missing transverse momentum $P_T^{miss}> 12\GeV$. In addition, a cut is applied on the  ratio $V_{ap}/V_p<0.35$. The quantities $V_{p}$ and $V_{ap}$ are respectively the transverse energy flow parallel and anti-parallel to the transverse momentum of the hadronic final state $\vec{P}_{T,h}$. The condition is tightened  $V_{ap}/V_p<0.15$ for events with  $P_T^{miss}<25$~GeV in order to reduce the photoproduction background. The photon virtuality $Q_h^2$ and the event inelasticity $y_h$, reconstructed from the hadronic final state, are restricted to the ranges $Q_h^2>1000\,\mathrm{GeV}^2$ and $0.1<y_h<0.9$, respectively. To exploit the expected energy loss due to the undetected neutrino,  a longitudinal energy imbalance is required $E-P_z<50\GeV$. 

The mass spectra measured for NC-like and CC-like events in the left- and righthanded data sets are shown in figure~\ref{fig:heraIIe-plots} for $e^-p$ collisions and in  figure~\ref{fig:heraIIe+plots} for $e^+p$ collisions.  Combined spectra for the $e^+p$ and $e^-p$ event samples including HERA I and HERA II data are shown in figure~\ref{fig:herae-e+plots}. The spectra obtained by combining all data sets presented in table~\ref{tab:datasets} are shown in figure~\ref{fig:heraplots}. 

The data are found to be in good agreement with the SM predictions, obtained using a Monte-Carlo simulation based on the DJANGO generator~\cite{DJANGO} and CTEQ5D parametrisation~\cite{cteq5d} of the proton parton densities.

No evidence for LQ production is observed in either the NC or CC
data samples. The mass spectra are therefore used to set constraints on LQs coupling to first generation fermions. Further sensitivity to the LQ production is obtained using the inelasticity variable $y$, related to the polar angle $\theta^\ast$ of the decay lepton in the centre-of-mass frame of the hard subprocess $(eq\rightarrow lq)$ by $y =\frac{1}{2}(1+\cos\theta^\ast)$. To make use of the different decay angle distributions for DIS and leptoquarks, all selected events are analysed in bins of varying size adapted to the experimental resolution in the $M-y$ plane, with a procedure designed to fully exploit the sensitivity to the signal. The statistical method is described in detail in~\cite{H1LQHERA1}.

\section*{Limit Results}

In the following limits are derived within the phenomenological model proposed by Buchm\"uller, R\"uckl and Wyler (BRW)~\cite{BRW}.
 
Table~\ref{tab:lqbrw} lists the 14 LQ types with fermion number $F=0$ and $F=2$  and their respective decays as described by the BRW model.
We use here the nomenclature of~\cite{LQNAME} to label the various scalar $S_{I,L}$ ($\tilde{S}^{\mbox{\tiny \hspace{-3mm}\raisebox{1.5mm}{(}\hspace{2mm}\raisebox{1.5mm}{)}}}_{I,R}$) or vector $\tilde{V}^{\mbox{\tiny
\hspace{-3mm}\raisebox{1.5mm}{(}\hspace{2mm}\raisebox{1.5mm}{)}}}_{I,L}$ ($V_{I,R}$) LQ types of weak isospin $I$, which couple to a left-handed (right-handed) electron. The tilde is used to distinguish LQs which differ only by their hypercharge. In the BRW model the branching ratios of the LQ types into electron--quark ($\beta_e$) and neutrino--quark ($\beta_{\nu}$) are fixed and equal to 1 or 0.5 ($\beta_e$) and 0 or 0.5 ($\beta_{\nu}$) depending on the LQ quantum numbers. 
% ------------------ TABLE : Scalar Leptoquarks  -------------------------
\begin{table*}[htb]
  \renewcommand{\doublerulesep}{0.4pt}
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 \vspace{-0.1cm}

\begin{center}
    \begin{tabular}{|c|r|c||c|r|c|}
      \hline
       $F=2$ & Prod./Decay & $\beta_e$
              & $F=0$ & Prod./Decay & $\beta_e$  \\

      \hline
%
% -> Scalar LQ :
     \multicolumn{6}{|c|}{Scalar Leptoquarks} \\ \hline
    $S_{0,L}$     & $e^-_L u_L \rightarrow e^- u$ & $1/2$
  & $S_{1/2,L}$   & $e^+_R u_R \rightarrow e^+ u$ & $1$  \\
                  &           $\rightarrow \nu d$ & $1/2$ & & & \\ \hline
    $S_{0,R}$     & $e^-_R u_R \rightarrow e^- u$ & $1$
  & $S_{1/2,R}$   & $e^+_L u_L \rightarrow e^+ u$ & $1$ \\
      \cline{1-3}
    $\tilde{S}_{0,R}$
                  & $e^-_R d_R \rightarrow e^- d$ & $1$
  &               & $e^+_L d_L \rightarrow e^+ d$ & $1$ \\
      \hline
    $S_{1,L}$     & $e^-_L d_L \rightarrow e^- d$ & $1$
  & $\tilde{S}_{1/2,L}$ 
                  & $e^+_R d_R \rightarrow e^+ d$ & $1$ \\
                  & $e^-_L u_L \rightarrow e^- u$ & $1/2$ & & &  \\
                  &           $\rightarrow \nu d$ & $1/2$ & & & \\
      \hline
%
% -> Vector LQ :
     \multicolumn{6}{|c|}{Vector Leptoquarks} \\ \hline
    $V_{1/2,R}$   & $e^-_R d_L \rightarrow e^- d$ & $1$
  & $V_{0,R}$     & $e^+_L d_R \rightarrow e^+ d$ & $1$ \\
      \cline{4-6}
                  & $e^-_R u_L \rightarrow e^- u$ & $1$
  & $V_{0,L}$     & $e^+_R d_L \rightarrow e^+ d$ & $1/2$ \\
            & & & &           $\rightarrow \overline{\nu}u$ & $1/2$ \\ \hline
    $V_{1/2,L}$   & $e^-_L d_R \rightarrow e^- d$ & $1$
  & $\tilde{V}_{0,R}$
                  & $e^+_L u_R \rightarrow e^+ u$ & $1$ \\
      \hline
    $\tilde{V}_{1/2,L}$
                  & $e^-_L u_R \rightarrow e^- u$ & $1$
  & $V_{1,L}$     & $e^+_R u_L \rightarrow e^+ u$ & $1$ \\
                          &                                            &
  &               & $e^+_R d_L \rightarrow e^+ d$ & $1/2$ \\
            & & & &           $\rightarrow \overline{\nu}u$ & $1/2$ \\
      \hline
      \hline
    \end{tabular}
    \caption {\small \label{tab:lqbrw}
               Leptoquark isospin families in the Buchm\"uller-R\"uckl-Wyler
               model.
               For each leptoquark, the subscript denotes its weak isospin
               and the chirality of the incoming {\it{electron}} which
               could mediate their production in $e^-p$ collisions.
               Charge conjugate processes are not shown.
               }
\end{center}
\end{table*}
% % ------------------------------------------------------------------------
% ------------------ TABLE : Scalar Leptoquarks  -------------------------
% \begin{table*}[htb]
%   \renewcommand{\doublerulesep}{0.4pt}
%   \renewcommand{\arraystretch}{1.2}
%  \vspace{-0.1cm}
% 
% \begin{center}
%     \begin{tabular}{|c|r|c|}
%       \hline
%        $F=2$ & Prod./Decay & $\beta_{e,nu}$\\
% 
%       \hline
% %
% % -> Scalar LQ :
%      \multicolumn{3}{|c|}{Scalar Leptoquarks} \\ \hline
%     $S_{0,L}$     & $e^-_L u_L \rightarrow e^- u$ & $1/2$\\
%                   &           $\rightarrow \nu d$ & $1/2$ \\ \hline
%     $S_{0,R}$     & $e^-_R u_R \rightarrow e^- u$ & $1$\\
%       \cline{1-3}
%     $\tilde{S}_{0,R}$
%                   & $e^-_R d_R \rightarrow e^- d$ & $1$\\
%       \hline
%     $S_{1,L}$     & $e^-_L d_L \rightarrow e^- d$ & $1$\\
%                   & $e^-_L u_L \rightarrow e^- u$ & $1/2$ \\
%                   &           $\rightarrow \nu d$ & $1/2$ \\
%       \hline
% %
% % -> Vector LQ :
%      \multicolumn{3}{|c|}{Vector Leptoquarks} \\ \hline
%     $V_{1/2,R}$   & $e^-_R d_L \rightarrow e^- d$ & $1$\\
%                   & $e^-_R u_L \rightarrow e^- u$ & $1$ \\
% \hline
%     $V_{1/2,L}$   & $e^-_L d_R \rightarrow e^- d$ & $1$ \\
%       \hline
%     $\tilde{V}_{1/2,L}$
%                   & $e^-_L u_R \rightarrow e^- u$ & $1$\\
%       \hline
%       \hline
%     \end{tabular}
%     \caption {\small \label{tab:lqbrw}
% Leptoquark isospin families with F=2 in the Buchm\"uller-R\"uckl-Wyler model. For each leptoquark, the subscript denotes its weak isospin and the chirality of the incoming electron which could mediate their production in $e^-p$ collisions. 
%                }
% \end{center}
%\end{table*}
% ------------------------------------------------------------------------
%

The resulting constraints are shown in fig.~\ref{fig:brw} for all 14 LQ types.
%the four scalar and in fig.~\ref{fig:brw}b for the three vector LQs with $F=2$. The areas above the curves are excluded at $95\%$ confidence level. 
The strongest constraints on the coupling $\lambda$ can be set for LQ masses below the kinematic limit of the $s$-channel. At higher masses, beyond HERA centre-of-mass energy,  the LQ production is not resonant  but proceeds via  contact interactions. In this region the LQ production cross section scales approximately with $(\lambda/M_{LQ})^4$. 
%For a coupling of electromagnetic strength $\alpha_{\rm em}$ ($\lambda = \sqrt{4\pi\alpha_{\rm em}}=0.3$) this analysis rules out LQ masses below $276$ to $304 \GeV$, depending on the LQ type.

The constraints obtained in the present analysis on the $\tilde{S}_{1/2,L}$ and   $S_{0,L}$ LQs are compared in figure~\ref{fig:brwcompar}  to the results obtained at  LEP~\cite{LQLEP1,LQLEP2} and Tevatron~\cite{d0}. Indirect constraints were obtained at LEP from $e^+e^- \rightarrow q \overline{q}$ process measurements. The limits from the Tevatron are independent of the coupling $\lambda$ as they were derived from the dominant pair production processes. The published H1 results~\cite{H1LQHERA1} from the HERA~I phase 
%(mainly $e^+ p$ running) 
are also shown for comparison. An unique domain is probed at HERA for LQ masses above Tevatron sensitivity and small coupling constants.
%Above the kinematic limit, the improvement w.r.t. to the HERA~I results is smaller than at lower masses, because the production is not resonant anymore and thus the sensitivities of the $e^+p$ and the $e^-p$ datasets (which have approximately the same integrated luminosity) to $F=2$ LQs are very similar. 
The limits on LQs also apply to squarks production is SUSY models with $R$-parity violation.
For instance, the $S_{0,L}$-like LQ also applies to squark $\tilde{d}_{k,R}$ with $R$-parity violating couplings $\lambda^\prime_{11k}$ to $eu$ and subsequent decays $\tilde{d}_{k,R}\rightarrow e^-u$ and $\tilde{d}_{k,R}\rightarrow \nu d$ (the subscript $k$ is a generation index here).

%Beyond the BRW ansatz, generic LQ models can also be considered, where
%other LQ decay modes are allowed such that the branching ratios $\beta_e$
%and $\beta_\nu$ are free parameters.
%Mass dependent constraints on the LQ branching ratios
%can then be set for a given value of $\lambda$.
%For a vector LQ coupling to $e^- u$ (possessing the
%quantum numbers of the $S_{0,L}$) and for $\lambda = 0.06$,
%the domain of the $\beta_e$-$M$ ($\beta_{\nu}$-$M$) plane
%excluded by the NC (CC) analysis is shown in Fig.~\ref{fig:betaeplus}a.
%If the LQ decays into $e q$ or $\nu q$
%only\footnote{It should be noted that $\beta_e + \beta_{\nu} = 1$ does
%   not imply $\beta_e = \beta_{\nu}$ even when
%   invariance under $SU(2)_L$ transformations is required.
%   For example, when LQs belonging to a given isospin multiplet are not
%   mass eigenstates, their mixing usually leads to different branching
%   ratios in both channels for the physical LQ states. },
%the combination of both channels rules out the part of the plane on 
%the left of the second full curve from the left for $\lambda = 0.06$. 
%The resulting combined bound is largely independent of the individual values
%of $\beta_e$ and $\beta_{\nu}$.
%Combined bounds are also shown for $\lambda=0.03$ and $\lambda=0.3$.
%For a coupling $\lambda=0.3$ and high $\beta_{\nu}$ the limit extends to high
% mass values above the kinematic limit of resonant LQ production.
% For this part of the parameter space the coupling
% $\lambda_{\nu}=\lambda\sqrt{\beta_\nu/\beta_e}$ is 
% large\footnote{In the BRW model, 
% $|\lambda_\nu|=|\lambda|$ since $\beta_\nu=\beta_e$. 
% Here, in a generic LQ model, the effective coupling
% $\lambda_\nu$ at the LQ-$\nu$-$q$ vertex can be different from $\lambda$
% at the LQ-$e$-$q$ vertex.},
% but still satisfies
% $\lambda_{\nu}^2/4\pi<1$.
% A smooth transition is observed
% between limits driven by resonant production and limits driven by contact
% interactions.
%The domain excluded by the D$0$ experiment at the Tevatron~\cite{d0} is 
%also shown. For $\lambda$ greater than $\sim 0.06$, 
%the H1 limits on scalar LQs extend considerably beyond the
%region excluded by the D$0$ experiment~\cite{d0}.

%The H1 limit on the $S_{0,L}$-like LQ applies to squark $\tilde{d}_i$ with $R$-parity violating couplings $\lambda^\prime_{11i}$ to $eu$ and subsequent decays $\tilde{d}_i\rightarrow e^-u$ and $\tilde{d}_i\rightarrow \nu d$ (the subscript $i$ is a generation index here).

%Similarly, the limit (unshown) on the $\tilde{S}_{1/2,L}$-like LQ also 
%applies to squark $\tilde{u}_i$ with 
%$R$-parity violating couplings $\lambda^\prime_{1i1}$ to $ed$ and 
%subsequent decay $\tilde{u}_i\rightarrow e^+d$.
%More general limits on squark production taking into account of direct and indirect $R$-parity violating decay modes have been set in~\cite{susylimit}.

To summarise, a search for leptoquarks production is performed using the polarised $e^-p$ and $e^+p$ data recorded by H1 at HERA II in the period 2003-2007. 
No signal is observed, in agreement with previous investigations at HERA I. The two analysis are combined  and 
%in combination with the full HERA~I data published in~\cite{H1LQ05} 
constraints on leptoquarks are set, which 
%for $F=2$ leptoquarks 
extend beyond the domains  previously excluded. 
%For a coupling of electromagnetic strength, leptoquark masses below $276-304$ GeV can be ruled out, depending on the leptoquark type.

\section*{Acknowledgements}
%
We are grateful to the HERA machine group whose outstanding
efforts have made this experiment possible.
We thank the engineers and technicians for their work in constructing 
and maintaining the H1 detector, our funding agencies for
financial support, the DESY technical staff for continual assistance
and the DESY directorate for support and for the
hospitality which they extend to the non DESY
members of the collaboration.

\begin{thebibliography}{99}

\bibitem{H1LQHERA1}
%\bibitem{H1LQ99}
%\cite{Aktas:2005pr}
%\bibitem{Aktas:2005pr}
  A.~Aktas {\it et al.}  [H1 Collaboration],
  %``Search for leptoquark bosons in e p collisions at HERA,''
  Phys.\ Lett.\  B {\bf 629} (2005) 9
  [hep-ex/0506044].
  %%CITATION = PHLTA,B629,9;%%

%  C.~Adloff {\it et al.}  [H1 Collaboration],
% %``A search for leptoquark bosons and lepton flavour violation in e+ p
% % collisions at HERA,''
% Eur.\ Phys.\ J.\ C {\bf 11} (1999) 447
% [Erratum-ibid.\ C {\bf 14} (1999) 553]
% [hep-ex/9907002].
% %%CITATION = HEP-EX 9907002;%%
% \vspace{-2mm}
% 
% \bibitem{H1LQHERA1_EMINUS}
% C.~Adloff {\it et al.} [H1 Collaboration],
% %``Measurement of neutral and charged current cross sections in electron
% % proton collisions at high Q**2,''
% Eur.\ Phys.\ J.\ C {\bf 19} (2001) 269
% [hep-ex/0012052].
% %%CITATION = HEP-EX 0012052;%%
% \vspace{-2mm}

\bibitem{h1det}
% H1 Collaboration, I.~Abt {\it et al.}, Nucl.\ Instrum.\ Meth.\ A386 (1997)
% 310 and 348.  -> No, 310 & 397
I.~Abt {\it et al.}  [H1 Collaboration],
%``The H1 detector at HERA,''
Nucl.\ Instrum.\ Meth.\ A {\bf 386} (1997) 310 and 348; \\
%%CITATION = NUIMA,A386,310;%%
%
R.~D.~Appuhn {\it et al.}  [H1 SPACAL Group],
%``The H1 lead/scintillating-fibre calorimeter,''
Nucl.\ Instrum.\ Meth.\ A {\bf 386} (1997) 397.
%%CITATION = NUIMA,A386,397;%%
\vspace{-2mm}
% \bibitem{H1LQe-}
% C.~Adloff {\it et al.}  [H1 Collaboration],
% %``A Search for Leptoquark Bosons in e^-p Collisions at HERA''
% Phys.\ Lett.\ B.\ {\bf 523} (2001) 234
% [hep-ex/0107038].
% %%CITATION = HEP-EX 0107038;%%
% \vspace{-2mm}

\bibitem{DJANGO}
 DJANGO~6.2;
 G.A.~Schuler and H.~Spiesberger,
 Proc. of the Workshop Physics at HERA,
 W.~Buchm\"uller and G.~Ingelman (Editors),
 (October 1991, DESY-Hamburg) Vol. 3 p. 1419.
\vspace{-2mm}

\bibitem{cteq5d}
H.~L.~Lai {\it et al.}  [CTEQ Collaboration],
%``Global {QCD} analysis of parton structure of the nucleon: CTEQ5 parton
%distributions,''
Eur.\ Phys.\ J.\ C {\bf 12} (2000) 375
[hep-ph/9903282].
%%CITATION = HEP-PH 9903282;%%
\vspace{-2mm}

\bibitem{BRW}
W.~Buchm\"uller, R.~R\"uckl and D.~Wyler,
%``Leptoquarks In Lepton Quark Collisions,''
Phys.\ Lett.\ B {\bf 191} (1987) 442
[Erratum-ibid.\ B {\bf 448} (1999) 320].
%%CITATION = PHLTA,B191,442;%%
\vspace{-2mm}

% \bibitem{bock}
% P.~Bock,
% %``Computation of confidence levels for exclusion or discovery of a signal with
% % the method of fractional event counting''
% [hep-ex/0405072].
% %%CITATION = HEP-EX 0405072;%%
% \vspace{-2mm}

% \bibitem{opallq}
% G.~Abbiendi {\it et al.} [OPAL Collaboration],
% %``Search for pair-produced leptoquarks in e interactions at sqrt(s)=189-209 GeV''
% Eur.\ Phys.\ J.\ C {\bf 31} (2003) 281.
% \vspace{-2mm}

% \bibitem{botje}
% M.~Botje,
% %``A QCD analysis of HERA and fixed target structure function data''
% Eur.\ Phys.\ J.\ {\bf C14} (2000) 285
% [hep-ph/9912439]; \newline http://www.nikhef.nl/{\small $\sim$}h24/qcdnum/ .
% %%CITATION = HEP-PH 9912439;%%
% \vspace{-2mm}

\bibitem{LQNAME}
%  B.~Schrempp, Proc. of the Workshop Physics at HERA,
%  DESY, Hamburg (1991), vol. 2 p. 1034, {\it and references therein}.
A.~Djouadi, T.~K\"ohler, M.~Spira and J.~Tutas,
%``(E B), (E T) Type Leptoquarks At E P Colliders,''
Z.\ Phys.\ C {\bf 46} (1990) 679.
%%CITATION = ZEPYA,C46,679;%%
\vspace{-2mm}

\bibitem{LQLEP1}
 G.~Abbiendi {\it et al.}  [OPAL Collaboration],
% %``Tests of the standard model and constraints on new physics from  measurements of fermion pair production at 183-GeV at LEP,''
 Eur.\ Phys.\ J.\ C {\bf 6} (1999) 1
 [hep-ex/9808023].
 %%CITATION = HEP-EX 9808023;%%
\vspace{-2mm}
\bibitem{LQLEP2}
M.~Acciarri {\it et al.}  [L3 Collaboration],
%``Search for Manifestations of New Physics in Fermion-Pair Production at LEP,''
Phys.\ Lett.\ B {\bf 486} (2000) 81
[hep-ex/0005028].
%%CITATION = HEP-EX 0005028%%
\vspace{-2mm}

\bibitem{d0}
%%CITATION = HEP-EX 9710032;%%
%
V.~M.~Abazov  [D0 Collaboration],
%``Search for first-generation scalar leptoquarks in p anti-p collisions at
%s**(1/2) = 1.96-TeV,''
Phys.\ Rev.\ D {\bf 71} (2005) 071104 
[hep-ex/0412029].
\vspace{-2mm}

% \bibitem{zeuslq}
% S.~Chekanov {\it et al.} [ZEUS Collaboration],
% %``Search for resonance decays to lepton+jet at DESY HERA and limits on leptoquarks''
% Phys.\ Rev.\ D {\bf 68} (2003) 052004.
% %%CITATION = ;%%
% \vspace{-2mm}

% \bibitem{ci}
% C.~Adloff {\it et al.}  [H1 Collaboration],
% %``Search for new Physics in e^\pm q contact interactions at HERA ''
% Phys.\ Lett.\ B {\bf 568} (2003) 35
% [hep-ex/0305015].
% %%CITATION = PHLTA,B568,35;%%
% \vspace{-2mm}

% \bibitem{nccc03}
% C.~Adloff {\it et al.}  [H1 Collaboration],
% %``Measurement and QCD Analysis of Neutral and Charged Current Cross Sections at HERA ''
% Eur.\ Phys.\ J.\ C {\bf 30} (2003) 1
% [hep-ex/0304003].
% %%CITATION = HEP-EX 0304003;%%
% \vspace{-2mm}

% \bibitem{susylimit}
% A.~Aktas {\it et al.}  [H1 Collaboration],
% %``Search for squark production in R-parity violating supersymmetry at HERA,''
% Eur.\ Phys.\ J.\ C {\bf 36} (2004) 425
% [hep-ex/0403027].
% %%CITATION = HEP-EX 0403027;%%

\end{thebibliography}

% % ---------- FIGURE 1: dNdM  Scalar and Vector  ----------------
% %
% \begin{figure}[p] 
% \begin{center}
% \begin{picture}(50,155)
% \put(-55,65){\epsfig{figure=H1prelim-06-061.fig1a.eps,width=8cm}}
% \put(0,110){\bf (a)}
% \put(25,65){\epsfig{figure=H1prelim-06-061.fig1b.eps,width=8cm}}
% \put(80,110){\bf (b)}
% \put(-55,0){\epsfig{figure=H1prelim-06-061.fig1c.eps,width=8cm}}
% \put(0,45){\bf (c)}
% \put(25,0){\epsfig{figure=H1prelim-06-061.fig1d.eps,width=8cm}}
% \put(80,45){\bf (d)}
% \end{picture}
% \end{center}
%   \caption{\label{fig:dndm}
% Mass spectra for the neutral current (a: left- and b: righthanded data sample) and the charged current (c: left- and d: righthanded data sample) events (points with error bars), together with the corresponding SM expectations (histogram). The shaded bands indicate the $\pm1\sigma$ uncertainty on the SM expectations.}
% \end{figure} 
% %---------------------------------------------------------------------------
% 
% % % ---------- FIGURE 2 weight  ----------------
% % %
% % \begin{figure}[p] 
% % \begin{center}
% % \begin{picture}(50,155)
% % %\put(-47.5,-5){\epsfig{figure=/afs/desy.de/user/z/zhang/h1raid8/paper/lq/figs/weight_v0l_m200_l023.eps,width=14cm}}
% % \put(-10,135){\bf NC}
% % \put(47,135){\bf CC}
% % %\put(20,137){\bf (a)}
% % %\put(20,90){\bf (b)}
% % %\put(20,45){\bf (c)}
% % %\put(77,137){\bf (d)}
% % %\put(77,90){\bf (e)}
% % %\put(77,45){\bf (f)}
% % \end{picture}
% % \end{center}
% %   \caption{\label{weight_bin}
% %   Binning used in the $M-y$ plane for the different datasets and
% %   weights calculated in these bins for a 200 GeV vector 
% %   leptoquark with a coupling of $0.023$ to $e^{+}d$ and $\bar{\nu}u$.
% %   The left plots correspond to the neutral current (NC) decay channel whereas
% %   the right plots correspond to the charged current (CC) decay channel. 
% %   The top, middle and bottom plots correspond to the $300$\,GeV $e^+p$,
% %   $320$\,GeV $e^-p$ and $320$\,GeV $e^+p$ data sets.}
% % \end{figure} 
% % %---------------------------------------------------------------------------
% 
% % --------------- FIGURE 3: Limits BRW : H1    --------------
% %
% \begin{figure}[p] 
% \begin{center}
% \begin{picture}(50,155)
% \put(-30,100){\epsfig{figure=H1prelim-06-061.fig2a.eps,width=12cm}}
% \put(65,125){(a)}
% \put(-30,0){\epsfig{figure=H1prelim-06-061.fig2b.eps,width=12cm}}
% \put(65,25){(b)}
% \end{picture}
% \end{center}
%   \caption{\label{fig:brw}
%   Exclusion limits for the 7 leptoquarks (LQs) with F=2 described by the
%   Buchm\"uller, R\"uckl and Wyler (BRW) model. The limits are expressed at
%   $95\%\,{\rm CL}$ on the coupling $\lambda$ as a function of 
%   the leptoquark mass for the (a) scalar LQs with $F=2$, 
%   (b) vector LQs with $F=2$.
%   Domains above the curves are excluded. For each LQ type the pairs of
%   Standard Model fermions coupling to it are indicated in brackets.}
% %  Constraints on LQs with masses above $580$\,GeV,
% %  obtained from the H1 contact interaction (CI) analysis~\cite{ci}, 
% %  are shown in the rightmost part of the figures.}
%   \end{figure} 
% %----------------------------------------------------------------------
% 
% % --------------- FIGURE 4: Limits BRW : H1 + LEP + D0    --------------
% %
% \begin{figure}[p]
% \begin{center}
% \begin{picture}(50,90)
% %%\put(-30,60){\epsfig{figure=/afs/desy.de/user/z/zhang/h1raid8/paper/lq/figs/h1_s12tl_lqepfinal_ciunshown_v4.eps,width=10.5cm}}
% %%\put(-30,-30){\epsfig{figure=/afs/desy.de/user/z/zhang/h1raid8/paper/lq/figs/h1_s0l_lqem_ciunshown_v4.eps,width=10.5cm}}
% %\put(-30,60){\epsfig{figure=/afs/desy.de/user/z/zhang/h1raid8/paper/lq/figs/h1_s12tl_lqepfinal_cifinal_v4.eps,width=10.5cm}}
% \put(-30,0){\epsfig{figure=H1prelim-06-061.fig3.eps,width=10.5cm}}
% \end{picture}
% \end{center}
%   \caption{\label{fig:brwcompar}
%   Exclusion limits at $95\%\,{\rm CL}$ on the coupling $\lambda$ as a function of the leptoquark (LQ) mass for $S_{0,L}$ in the framework of the BRW model. The indirect limit from L3 and the direct D0 limits are shown for comparision. For comparison, the published H1 limit on $S_{0,L}$ from HERA~I data is shown in addition.}
% \end{figure} 
% %----------------------------------------------------------------------
% 
% % --------------- FIGURE 5 : Limits beta vs mass  -------------------------
% %
% \begin{figure}[p] 
% \begin{center}
% \begin{picture}(50,105)
% %\put(-30,-5){\epsfig{figure=/afs/desy.de/user/z/zhang/h1raid8/paper/lq/figs/betavec.eps,width=10cm}}
% \end{picture}
% \end{center}
%   \caption{\label{fig:betaeplus}
%   Domains ruled out by the combination of the NC and CC analyses, for a scalar LQ coupling to $e^-u$ (with the quantum numbers of the $S_{0,L}$). The regions on the left of the full curves are excluded at $95\%\,{\rm CL}$.
%   For $\lambda=0.06$, the part of the $\beta_e-M_{\rm LQ}$ 
%   ($\beta_\nu-M_{\rm LQ}$) plane on the left of the dashed (dotted) curve is excluded by the NC (CC) analysis alone. The branching ratios $\beta_e$ and $\beta_\nu(=1-\beta_e)$ are shown on the left and right axes respectively. 
%   In (b), the hatched region represents the domain excluded by the D0 
%   experiment. The D0 limits do not depend on the value 
%   of the coupling.}
% \end{figure} 
% %----------------------------------------------------------------------



\begin{figure}
  \begin{center}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig1a.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig1b.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig1c.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig1d.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (1.7,9.9){\bf\large a)}
    \put (9.7,9.9){\bf\large b)}
    \put (1.7,4.2){\bf\large c)}
    \put (9.7,4.2){\bf\large d)}
%    \put (6.6,11.4){\bf\large a)}
%    \put (14.5,11.4){\bf\large b)}
%    \put (6.6,5.6){\bf\large c)}
%    \put (14.5,5.6){\bf\large d)}
  \end{picture}

  \caption{Reconstructed LQ mass spectra of the HERA~II $e^{-}p$ data for Neutral  Current (a: left- and b: righthanded data) and Charged Current (c:
  left- and d: righthanded data) events. The points represent the data and are compared to the SM
  expectation (histogram). The shaded band indicates the uncertainty
  on the SM expectation. The average polarisation of each data set is
  also indicated.}

  \label{fig:heraIIe-plots}
\end{figure}

\clearpage

\begin{figure}
  \begin{center}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig2a.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig2b.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig2c.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig2d.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (1.7,9.9){\bf\large a)}
    \put (9.7,9.9){\bf\large b)}
    \put (1.7,4.2){\bf\large c)}
    \put (9.7,4.2){\bf\large d)}
%    \put (6.6,11.4){\bf\large a)}
%    \put (14.5,11.4){\bf\large b)}
%    \put (6.6,5.6){\bf\large c)}
%    \put (14.5,5.6){\bf\large d)}
  \end{picture}

  \caption{Reconstructed LQ mass spectra of the HERA~II $e^{+}p$ data for Neutral
  Current (a: left- and b: righthanded data) and Charged Current (c:
  left- and d: righthanded data) events. The points represent the data and are compared to the SM
  expectation (histogram). The shaded band indicates the uncertainty
  on the SM expectation. The average polarisation of each data set is
  also indicated.}
  \label{fig:heraIIe+plots}
\end{figure}

\clearpage

\begin{figure}
  \begin{center}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig3a.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig3b.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig3c.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig3d.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (1.7,9.9){\bf\large a)}
    \put (9.7,9.9){\bf\large b)}
    \put (1.7,4.2){\bf\large c)}
    \put (9.7,4.2){\bf\large d)}
%    \put (6.6,11.4){\bf\large a)}
%    \put (14.5,11.4){\bf\large b)}
%    \put (6.6,5.6){\bf\large c)}
%    \put (14.5,5.6){\bf\large d)}
  \end{picture}

  \caption{Mass spectra of the complete HERA I+II data for Neutral
  Current (a: $e^{-}p$ data and b: $e^{+}p$ data) and Charged Current
  (c: $e^{-}p$ data and d: $e^{+}p$ data) events in the H1 leptoquark
  analysis. The points are the data, which are compared to the SM
  expectation (histogram). The shaded band indicates the uncertainty
  on the SM expectation.}

  \label{fig:herae-e+plots}
\end{figure}

\clearpage

\begin{figure}
  \begin{center}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig4a.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig4b.eps}
  \end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (1.7,4.6){\bf\large a)}
    \put (9.7,4.6){\bf\large b)}
  \end{picture}

  \caption{Mass spectra of the complete HERA I+II $e^{\pm}p$ data for
  Neutral Current (a) and Charged Current (b) events in the H1
  leptoquark analysis. The points are the data, which are compared to
  the SM expectation (histogram). The shaded band indicates the
  uncertainty on the SM expectation.}

  \label{fig:heraplots}
\end{figure}

\begin{figure}[p] 
\begin{center}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig5a.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig5b.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig5c.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig5d.eps}
\end{center}
  \begin{picture} (0.,0.)
  \setlength{\unitlength}{1.0cm}
    \put (1.7,9.9){\bf\large a)}
    \put (9.7,9.9){\bf\large b)}
    \put (1.7,4.2){\bf\large c)}
    \put (9.7,4.2){\bf\large d)}
%    \put (6.6,11.4){\bf\large a)}
%    \put (14.5,11.4){\bf\large b)}
%    \put (6.6,5.6){\bf\large c)}
%    \put (14.5,5.6){\bf\large d)}
  \end{picture}
  \caption{\label{fig:brw}
  Exclusion limits for the 14 leptoquarks (LQs) with F=2 and   F=0 described by the
  Buchm\"uller, R\"uckl and Wyler (BRW) model. The limits are expressed on the coupling $\lambda$ as a function of 
  the leptoquark mass for the (a) scalar LQs with $F=0$, 
  (b) vector LQs with $F=0$ (c)  vector LQs with $F=2$ and (d)  scalar LQs with $F=2$.
  Domains above the curves are excluded at
  $95\%\,{\rm CL}$. For each LQ type the pairs of
  Standard Model fermions coupling to it are indicated in brackets.}
%  Constraints on LQs with masses above $580$\,GeV,
%  obtained from the H1 contact interaction (CI) analysis~\cite{ci}, 
%  are shown in the rightmost part of the figures.}
  \end{figure} 

\begin{figure}[p]
\begin{center}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig6a.eps}
      \includegraphics[width=.49\textwidth]{H1prelim-07-164.fig6b.eps}

\end{center}
  \caption{\label{fig:brwcompar}
  Exclusion limits at $95\%\,{\rm CL}$ on the coupling $\lambda$ as a function of the leptoquark mass for $\tilde{S}_{0,L}$ (left) and $S_{0,L}$ (right) in the framework of the BRW model. The indirect limit from LEP (OPAL and L3) and the direct limits from Tevatron (D0) are shown for comparision. The published H1 limit from HERA~I data is also shown.}
\end{figure} 

\end{document}
