Searches at HERA
Nicolas Delerue
(on behalf of the H1 and ZEUS collaborations)
Searches for physics beyond the Standard Model have been performed in high-energy $e^{\pm}p$ collisions at HERA. No significant deviation from the Standard Model has been observed while searching for contact interactions, extra dimensions, leptoquarks, R-parity violating squarks and excited fermions. Exclusion limits have been inferred which extend or complement bounds from other colliders. The H1 collaboration has observed a puzzling excess of events with an high $P_t$ isolated lepton and missing transverse momentum, and interpretation as flavour changing neutral currents has been explored.
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\newcommand{\rp}{\mbox{$\not \hspace{-0.15cm} R_p$} }

\begin{document}

\title{Searches at HERA}

\author{Nicolas Delerue\\(on behalf of the H1 and ZEUS collaborations)}

\address{Centre de Physique des Particules de Marseille\\
163, avenue de Luminy,\\
Case 907,\\
F-13288 Marseille Cedex 9\\
France\\
E-mail: \tt nicolas.delerue@desy.de}

\maketitle

\abstracts{Searches for physics beyond the Standard Model have been performed in high-energy $e^{\pm}p$ collisions at HERA. No significant deviation from the Standard Model has been observed while searching for contact interactions, extra dimensions, leptoquarks, R-parity violating squarks and excited fermions. Exclusion limits have been inferred which extend or complement bounds from other colliders. The H1 collaboration has observed a puzzling excess of events with an high $P_t$ isolated lepton and missing transverse momentum, and interpretation as flavour changing neutral currents has been explored.}

\section{Introduction}
 
\subsection{HERA}
HERA is the first and only existing lepton-proton collider. Between 1994 and 2000 it has delivered an integrated luminosity of more than 130 pb$^{-1}$ available for physics to each experiment. Leptons (electrons or positrons) have an energy of 27.6 GeV and protons have an energy of 920 GeV (or 820~GeV), this gives an energy in the centre of mass ($\sqrt{s}$) of 318 GeV (or 300~GeV). 
% There have been three main running periods. Between 1994 and 1997, positron-proton collisions were performed with a proton energy of 820 GeV. In 1998 and early 1999, electron-proton collisions were done with a proton energy of 920 GeV. From mid 1999 till the end of 2000, positron-proton collisions were done with a proton energy of 920 GeV. 
The HERA collider is now shut down for a luminosity upgrade.

\subsection{Physics at HERA}

%\begin{figure}[htbp]
%\begin{center}
%\epsfig{file=dis_diag.eps,height=6cm,angle=270} % postscript image file name
%\end{center}
%\caption{Feynman diagram of a DIS at HERA \label{diag:dis}}
%\end{figure}

One of the major Standard Model (SM) physics processes at HERA is  deep inelastic scattering (DIS) where the incoming lepton exchanges a gauge boson with a quark of the proton. 
% The variable $x$ denotes the fraction of the proton momentum carried by the struck quark, $y$ denotes the angular distribution and $Q^2$, defined as the opposite of the transfered four-momentum ($q^2$), is the spatial resolution. 
Neutral Current (NC) events result from the exchange of a neutral ($\gamma$,$Z^0$) boson and yield an electron and a recoil jet in the final state, Charged Current (CC) events result from the exchange of a charged  ($W^{\pm}$) boson and yield a neutrino and a recoil jet in the final state.

%If the exchanged boson is neutral ($\gamma/Z^o$), then the event is called ``Neutral Current'' (NC) and there is an electron and a recoil jet in the final state.  If the exchanged boson is charged ($W^{\pm}$), then the event is called ``Charged Current'' (CC) and there is a recoil jet and missing transverse momentum in the final state. 


%A full description of the apparatus can be found in~\cite{h1dete} for the H1 detector and in~\cite{zeusDete} for the ZEUS detector.
%\subsection{The H1 detector}
%\subsection{The ZEUS detector}



\section{Inclusive NC DIS events at high $Q^2$}

Phenomena characterised by a mass scale $\Lambda$ larger than HERA's kinematic limit ($\sqrt{s} \simeq 318 $ GeV) can be parameterised by four-fermion interactions which could affect the cross-sections for DIS observed at HERA via contact interactions. Comparisons of the cross-section predicted by the SM and those observed at high $Q^2$ at HERA have been made by both collaborations~\cite{Adloff:2000dp,Breitweg:2000ssa}. No deviations have been observed for $Q^2$ up to 10,000 GeV$^2$. Thus, exclusion limits in various contact interaction models can be set on $\Lambda$ up to 9 GeV with the usual coupling strength convention of $\sqrt{4\pi}$. 
Limits on large extra dimensions have also been set by H1 and exclude scale parameters ($M_s$) lower than 0.63 TeV and 0.93 TeV for positive and negative interference, respectively.

\section{Leptoquarks}

Leptoquarks are scalar or vector bosons  which couple to a quark and a lepton via a Yukawa coupling $\lambda$. They can be resonantly produced at HERA.  Their final topology  is the same as NC or CC events but their angular distribution can be used to optimise the signal significance.

It had been shown earlier~\cite{Adloff:1999tp,Breitweg:2000sa} that the HERA data collected in 1994-97 showed an excess of electron-quark masses greater than 200 GeV (figure~\ref{fig:lqMassPlot}, left). This excess is not confirmed in the new data collected by both experiments\cite{osk-953,osk-1038,osk-954} (figure~\ref{fig:lqMassPlot}, right).

\begin{figure}[htbp]
\begin{center}
\begin{tabular}{cc}
\epsfig{file=lq9497mass.eps,width=4.cm}&\epsfig{file=lq9900mass.eps,width=4.cm}
\end{tabular}
\end{center}
\vspace*{-.5cm}
\caption{The mass distribution of observed NC-DIS events compared to the  expected background for the 1994-1997 data (left) and 1999-2000 data (right).\label{fig:lqMassPlot}}
\vspace*{-.5cm}
\end{figure}


\begin{figure}[htbp]
\begin{center}
\begin{tabular}{c}
\epsfig{file=LQ_ZEUS_e-p.eps,width=7.5cm}
\vspace{2cm}\\
\hspace*{-2cm}\epsfig{file=LQ_ZEUS_fig11b.eps,width=8.cm}
\end{tabular}
\end{center}
\vspace*{2cm}
\caption{\label{fig:lqLimPlot} Limits on the Yukawa coupling in the BRW model (upper plot) and limits on the branching ratio $ LQ \rightarrow eq $ versus mass for fixed values of $\lambda$ (lower plot).}
\vspace*{-.5cm}
\end{figure}


As no excess is seen, limits have been derived by both collaborations. The results have been interpreted in the model of Buchm\"uller, R\"uckl and Wyler (BRW)~\cite{Buchmuller:1987zs} where the leptoquark branching ratios are fixed.
 The upper plot of figure~\ref{fig:lqLimPlot} shows the limits set by both collaborations in the BRW framework. The lower plot shows the limits derived in a more general model for fixed values of the coupling\cite{Breitweg:2001ks}.

\section{\rp supersymmetry}

$R_p$-violating squarks can be produced at HERA up to the kinematic limit in the same way as leptoquarks. They would have many possible decay modes and many different topologies, including some very striking, almost background-free, topologies such as events with a lepton whose charge is opposite to that one of the incoming lepton, or with multileptons.

The signal was looked for in almost all decay modes and no excess was observed~\cite{Adloff:2001at,osk-1042}. Upper limits on the Yukawa coupling $\lambda_{1j1}'$ have been obtained as a function
    of the squark mass (see figure~\ref{fig:SUSY}, left), by performing
    a scan in the parameters of the Minimal
    Supersymmetric Standard Model (MSSM). For a coupling 
    of the electromagnetic strength, squark masses below 258 GeV
are ruled out.
    Constraints on the parameters of the
mSUGRA
% minimal    Supergravity
 model are also shown in figure~\ref{fig:SUSY} (right) for
     specific values of the Yukawa coupling.

\begin{figure}[htbp]
\begin{center}
\begin{tabular}{cc}
\epsfig{file=SUSY_ZEUS_scan.eps,width=6.cm}&
\epsfig{file=SUSY_H1_MSUGRApaper.eps,width=6.cm}\\
\end{tabular}
\end{center}
\vspace*{-.5cm}
\caption{{\it Left:} Limits on $\lambda'_{1j1}$ as a function of the squark mass for the unconstrained MSSM. For each $\tan \beta$ hypothesis (dark lines for $\tan \beta = 2$ and light gray lines for $\tan \beta = 10$), the best and worse limit found during the scan are shown
%; as squark production at HERA is quite model independent, the two lines are close for each $\tan \beta$ hypothesis. 
{\it Right:} Domain of the plane ($m_0,m_{1/2}$) excluded by the H1 analysis for $\mu < 0$ and $\tan \beta = 6$ for a \rp coupling of $\lambda'_{1j1} = 0.3 $ (light shaded area) and  $\lambda'_{1j1} = 0.1 $ (dark grey area). The region below the dashed curve corresponds to the area excluded by the D0 experiment.\label{fig:SUSY}}
\vspace*{-.5cm}
\end{figure}

\section{Excited fermions}

Compositeness could manifest in excited states of fermions. The single production of excited fermions is considered at HERA. An effective Lagrangian~\cite{Kuhn:1984rj,Hagiwara:1985wt} describes the production and decay of excited fermions. In this Lagrangian, $\Lambda$~is the compositeness scale and $f$, $f'$ and $f_s$ are form factors which determine the couplings of a fermion to its corresponding excited states and to the bosons associated to the three gauge groups (SU(2), U(1) and SU(3)).

%\begin{eqnarray*}
% {{\cal{L}}_{int}}  =  \frac{1}{2 \Lambda} F^*_R \sigma^{\mu \nu} \left[ g{f} \frac{\tau^a}{2} {W_{\mu \nu}^a } + g'{f'} \frac{Y}{2} {B_{\mu \nu} } + g_s {f_s} \frac{\lambda ^a}{2} {G_{\mu \nu}^a } \right] F_L + h.c
%\end{eqnarray*}
%
%where  $W_{\mu \nu}^a$, {$B_{\mu \nu}$} are {$G_{\mu \nu}^a$} the tensors associated to the jauge fields {$SU(2)$}, {$U(1)$} and {$SU(3)_C$}, {$\Lambda$} is the scale of the substructure and {$f$}, {$f'$} and {$f_s$} are form factors associated to the three jauge groups.

The search in the data collected at $\sqrt{s} = 300 $ GeV between 1994 and 1997 has been completed~\cite{Adloff:2000gv,osk-1040} and no signal was found, thus limits have been inferred (see figure~\ref{fig:EXq}). By assuming $\frac{f}{\Lambda} = \frac{1}{M^*}$ one can exclude excited electrons of mass $M^*$ lower than 229 GeV and excited quarks of mass lower than 203 GeV.

\begin{figure}[htbp]
\begin{center}
\vspace*{-2.3cm}
\begin{tabular}{ccc}
\hspace*{1cm}\epsfig{file=estar_h1_zeus.eps,width=3.7cm}&
\epsfig{file=qstar_h1_zeus.eps,width=3.7cm}&
\hspace*{-1.4cm}\epsfig{file=EXCIT_H1_f_lim.eps,width=4.cm}
\end{tabular}
\end{center}
\caption{{\it Left:} Limits on the coupling constant as a function of the mass of the excited electron. {\it Center:} Limit on the coupling constant as a function of the mass of the excited quark. {\it Right:} Limit on the form factor $f$ as a function of the mass of the excited quark, with the hypothesis $f=f'$ and $\Lambda = M(q^*)$ for various values of the form factor $f_s$.\label{fig:EXq}}
\vspace*{-.5cm}
\end{figure}


The production cross-section for excited neutrinos ($\nu^*$) is higher (by two orders of magnitude for a $\nu^*$ of 200 GeV) in $e^-p$ data than in $e^+p$ data. Preliminary results show that no evidence for $\nu^*$ production has been found by either collaboration~\cite{osk-1040,osk-956} in the recently taken $e^-p$ data. Limits have thus been inferred (see figure~\ref{fig:EXnu}). 
%With the coupling found here, at 220 GeV, the intrisic width of the excited neutrino is of the order of 20 GeV and thus the narrow width approximation (NWA) assumed by the generator becomes less accurate and a band reflecting the uncertainty due to this use of the NWA has been added on the H1 limit. 
By assuming $\frac{f}{\Lambda} = \frac{1}{M^*}$ one can exclude excited neutrinos  of mass below 150 GeV for $f=-f'$ and below 134 GeV for $f=+f'$. As one can see on the figures~\ref{fig:EXq} (center) and \ref{fig:EXnu}, the limits set at HERA reach higher energies than those set at LEP. On figure~\ref{fig:EXq}, the plot on the right shows that for small $f_s$ HERA can extend the limits set at the TeVatron on the excited quark coupling.

\begin{figure}[tbp]
\vspace*{-.6cm}
\begin{center}
\begin{tabular}{cc}
\epsfig{file=folAll-combi-fminf-col.eps,width=3.5cm}&
\epsfig{file=limComb+fp-col.eps,width=3.5cm}
\end{tabular}
\end{center}
\vspace*{-.7cm}
\caption{Limits on the coupling constant as a function of the mass of the excited neutrino for the hypothesis $f=-f'$ (left) and $f=+f'$ (right). \label{fig:EXnu}}
%The hatched band reflects the uncertainty due to the use of the NWA.
\vspace*{-.5cm}
\end{figure}

\section{Events with an isolated lepton and missing transverse momentum, FCNC}

Puzzling events with high $P_t$ isolated lepton and missing transverse momentum have been previously observed at HERA. In the SM, such final states mainly come from W production. Both collaborations 
%~\cite{Adloff:1998aw,Breitweg:2000ie}
%have agreed on a common set of cuts in order to 
have a comparable analysis~\cite{osk-974,osk-1041} (see table~\ref{tab:isol}). H1 still sees a deviation from the SM prediction whereas ZEUS does not and this needs to be resolved with more statistics. Beyond the SM, an explanation of these events could be flavour changing neutral currents (FCNC) leading to single top production which is highly suppressed in the SM. 
%As, even if deviations from the SM have been observed, there is no evidence for FCNC leading to single top production, 
Limits on this phenomena have been set by both collaborations~\cite{osk-1041,osk-961} (see figure \ref{fig:top}).

\begin{table}
\begin{center}
\begin{tabular}{|c||c|c|c|c||}
\hline
          &   H1 data & \multicolumn{2}{|c|}{SM expectation } & ZEUS data \\
 & preliminary & H1 & ZEUS & preliminary \\
%\hline
%Luminosity &  82 pb$^{-1}$   & & &  82 pb$^{-1} $   \\
%\hline
%Dataset & 1994 to may 2000 & & & 1994 to 1999 \\
%\hline
\hline
$P^X_T (e)  > 25 $ GeV & 3  & $ 0.84 $ & $ 0.78 $ & 1 \\ 
\hline
$P^X_T (\mu)  > 25 $ GeV & 6  &\hspace*{.1cm} $ 0.94 $\hspace*{.1cm} &\hspace*{.1cm} $ 0.82 $\hspace*{.1cm} & 0 \\ 
\hline
%\hline
\end{tabular}
\end{center}
\caption{Comparison of the numbers of  events with high $P_t$ isolated leptons compared to the Standard Model expectation. The results presented here correspond, for both collaborations, to $ 82 pb^{-1}$ analysed before July 2000. In the H1 numbers, further cuts were applied after the nominal selection cuts such that both analyses correspond to similar acceptances for W events.\label{tab:isol}}
\vspace*{-.5cm}
\end{table}



\begin{figure}[htbp]
\vspace*{-2.cm}
\begin{center}
\epsfig{file=top.limits.eps,width=6.cm}
\end{center}
\caption{Limits on the anomalous $tu\gamma$ (magnetic) coupling $\kappa_{\gamma,u}$ and on the anomalous $tuZ$ (vector) coupling $\sqrt{a^2_Z+v^2_Z}$ obtained at the TeVatron (CDF), LEP (ALEPH) and HERA (H1 and ZEUS) colliders.\label{fig:top}}
\vspace*{-.5cm}
\end{figure}

\section{Conclusion}

Searches have been performed for contact interactions, extra dimensions, leptoquarks, \rp supersymmetry and excited fermions and no evidence was found for any of these processes. Limits have thus been derived and are comparable to those set at LEP or the TeVatron. The isolated lepton events observed by H1 are still puzzling. HERA is currently being upgraded to produce 5 times more luminosity starting this autumn (2001), thus searches have an exciting future at HERA.

\section*{Acknowledgments}

\vspace*{-.2cm}

I wish to thank all my ZEUS and H1 colleagues who have contributed to the results discussed here.

\begin{thebibliography}{99}

\vspace*{-.2cm}

%\cite{Abt:1997hi}
%\bibitem{h1dete}
%I.~Abt {\it et al.}  [H1 Collaboration],
%``The H1 detector at HERA,''
%Nucl.\ Instrum.\ Meth.\ A {\bf 386} (1997) 310.
%#%CITATION = NUIMA,A386,310;%%

%\cite{unknown:1993ee}
%\bibitem{zeusDete}
%  [ZEUS Collaboration],
%``The ZEUS detector: Status report 1993,''
%ZEUS-STATUS-REPT-1993.

%CI H1
%\cite{Adloff:2000dp}
\bibitem{Adloff:2000dp}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``Search for compositeness, leptoquarks and large extra dimensions in e q  contact interactions at HERA,''
Phys.\ Lett.\ B {\bf 479} (2000) 358
[hep-ex/0003002].
%%CITATION = HEP-EX 0003002;%%
H1 Collaboration, Abstract {\bf 951}, submitted to ICHEP 2000, Osaka.

%LQ, CI ZEUS
%\cite{Breitweg:2000ssa}
\bibitem{Breitweg:2000ssa}
J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``Search for contact interactions in deep inelastic e+ p $\to$ e+ X  scattering at HERA,''
Eur.\ Phys.\ J.\ C {\bf 14} (2000) 239
[hep-ex/9905039].
%%CITATION = HEP-EX 9905039;%%


%\bibitem{osk-1038} ZEUS Collaboration, contributed paper {\bf 1038 }, %``Comparison of ZEUS 1994-2000 data with standard model predictions for $e^{\pm} \rightarrow e^{\pm}X$ scattering at high $x$ and $Q^2$, 
%ICHEP 2000, Osaka, 27th of July - 2nd of August 2000.

%\cite{Adloff:1999tp}
\bibitem{Adloff:1999tp}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``A search for leptoquark bosons and lepton flavor violation in e+ p  collisions at HERA,''
Eur.\ Phys.\ J.\ C {\bf 11} (1999) 447
[hep-ex/9907002].
%%CITATION = HEP-EX 9907002;%%

%\cite{Breitweg:2000sa}
\bibitem{Breitweg:2000sa}
J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``Search for resonances decaying to e+ jet in e+ p interactions at HERA,''
Eur.\ Phys.\ J.\ C {\bf 16} (2000) 253
[hep-ex/0002038].
%%CITATION = HEP-EX 0002038;%%

%LQ H1
\bibitem{osk-953} 
H1 Collaboration, Abstract {\bf 953}, submitted to ICHEP 2000, Osaka.
%``Search for Leptoquarks in $ep$ collisions at HERA'' 

%LQ ZEUS
\bibitem{osk-1038} 
ZEUS Collaboration, Abstract {\bf 1038}, submitted to ICHEP 2000, Osaka.
%``Search for Leptoquarks in $ep$ collisions at HERA'' 


%LQ e-p H1
\bibitem{osk-954} 
H1 Collaboration, Abstract {\bf 954}, submitted to ICHEP 2000, Osaka.\\
ZEUS Collaboration, Abstract {\bf 552} submitted to EPS HEP 1999, Tampere.
%``A Search for Leptoquark Bosons in $e^-p$ Collisions at HERA'' 

%\cite{Buchmuller:1987zs}
\bibitem{Buchmuller:1987zs}
W.~Buchmuller, R.~Ruckl and D.~Wyler,
%``Leptoquarks in lepton quark collisions,''
Phys.\ Lett.\ B {\bf 191} (1987) 442.
%%CITATION = PHLTA,B191,442;%%
Erratum-ibid.B448:320,1999 

%\cite{Breitweg:2001ks}
\bibitem{Breitweg:2001ks}
J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``A search for resonance decays to anti-nu jet in e+ p scattering at  HERA,''
Phys.\ Rev.\ D {\bf 63} (2001) 052002
[hep-ex/0009059].
%%CITATION = HEP-EX 0009059;%%


%SUSY H1
%Osaka 957
%\cite{Adloff:2001at}
\bibitem{Adloff:2001at}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``Searches at HERA for squarks in R-parity violating supersymmetry,''
hep-ex/0102050.
DESY-01-021, Submitted to Eur.Phys.J.C 
%%CITATION = HEP-EX 0102050;%%

%SUSY ZEUS
\bibitem{osk-1042} 
ZEUS Collaboration, Abstract {\bf 1042}, submitted to ICHEP 2000, Osaka.
%``Search for squark production in R-parity violating interactions at HERA, 

%\cite{Kuhn:1984rj}
\bibitem{Kuhn:1984rj}
J.~Kuhn and P.~Zerwas,
%``Excited Quarks And Leptons,''
Phys.\ Lett.\ B {\bf 147} (1984) 189.
%%CITATION = PHLTA,B147,189;%%

%\cite{Hagiwara:1985wt}
\bibitem{Hagiwara:1985wt}
K.~Hagiwara, D.~Zeppenfeld and S.~Komamiya,
%``Excited Lepton Production At Lep And Hera,''
Z.\ Phys.\ C {\bf 29} (1985) 115.
%%CITATION = ZEPYA,C29,115;%%


%\cite{Adloff:2000gv}
\bibitem{Adloff:2000gv}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``A search for excited fermions at HERA,''
Eur.\ Phys.\ J.\ C {\bf 17} (2000) 567
[hep-ex/0007035].
%%CITATION = HEP-EX 0007035;%%

%f* ZEUS
\bibitem{osk-1040} 
ZEUS Collaboration, Abstract {\bf 1040}, submitted to ICHEP 2000, Osaka.
%``Search for excited fermions in $ep$ collisions at HERA'', 

%excited nu* H1
\bibitem{osk-956} 
H1 Collaboration, Abstract {\bf 956}, submitted to ICHEP 2000, Osaka.
%``A Search for Excited Neutrinos in $e^-p$ Collisions at HERA'',  


%\cite{Adloff:1998aw}
%\bibitem{Adloff:1998aw}
%C.~Adloff {\it et al.}  [H1 Collaboration],
%``Observation of events with an isolated high energy lepton and missing  transverse momentum at HERA,''
%Eur.\ Phys.\ J.\ C {\bf 5} (1998) 575
%[hep-ex/9806009].
%#%CITATION = HEP-EX 9806009;%%

%\cite{Breitweg:2000ie}
%\bibitem{Breitweg:2000ie}
%J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``W production and the search for events with an isolated high-energy  lepton and missing transverse momentum at HERA,''
%Phys.\ Lett.\ B {\bf 471} (2000) 411
%[hep-ex/9907023].
%#%CITATION = HEP-EX 9907023;%%


%w prod H1
\bibitem{osk-974} 
H1 Collaboration, Abstract {\bf 974}, submitted to ICHEP 2000, Osaka.
%``W production in ep collisions at HERA''

%isol lepton ZEUS
\bibitem{osk-1041} 
H1 Collaboration, Abstract {\bf 1041}, submitted to ICHEP 2000, Osaka.
%``Search for events with isolated high-energy leptons and missing transverse momentum at HERA''

%single top H1
\bibitem{osk-961} 
H1 Collaboration, Abstract {\bf 961}, submitted to ICHEP 2000, Osaka.
%``Search for Single Top Production in $e^{\pm}p$ collisions at HERA, 

\end{thebibliography}

\end{document}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% End of  ws-p8-50x6-00.tex  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


hep-ex0107039.extracted_bib
\begin{thebibliography}{99}

\vspace*{-.2cm}

%\cite{Abt:1997hi}
%\bibitem{h1dete}
%I.~Abt {\it et al.}  [H1 Collaboration],
%``The H1 detector at HERA,''
%Nucl.\ Instrum.\ Meth.\ A {\bf 386} (1997) 310.
%#%CITATION = NUIMA,A386,310;%%

%\cite{unknown:1993ee}
%\bibitem{zeusDete}
%  [ZEUS Collaboration],
%``The ZEUS detector: Status report 1993,''
%ZEUS-STATUS-REPT-1993.

%CI H1
%\cite{Adloff:2000dp}
\bibitem{Adloff:2000dp}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``Search for compositeness, leptoquarks and large extra dimensions in e q  contact interactions at HERA,''
Phys.\ Lett.\ B {\bf 479} (2000) 358
[hep-ex/0003002].
%%CITATION = HEP-EX 0003002;%%
H1 Collaboration, Abstract {\bf 951}, submitted to ICHEP 2000, Osaka.

%LQ, CI ZEUS
%\cite{Breitweg:2000ssa}
\bibitem{Breitweg:2000ssa}
J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``Search for contact interactions in deep inelastic e+ p $\to$ e+ X  scattering at HERA,''
Eur.\ Phys.\ J.\ C {\bf 14} (2000) 239
[hep-ex/9905039].
%%CITATION = HEP-EX 9905039;%%


%\bibitem{osk-1038} ZEUS Collaboration, contributed paper {\bf 1038 }, %``Comparison of ZEUS 1994-2000 data with standard model predictions for $e^{\pm} \rightarrow e^{\pm}X$ scattering at high $x$ and $Q^2$, 
%ICHEP 2000, Osaka, 27th of July - 2nd of August 2000.

%\cite{Adloff:1999tp}
\bibitem{Adloff:1999tp}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``A search for leptoquark bosons and lepton flavor violation in e+ p  collisions at HERA,''
Eur.\ Phys.\ J.\ C {\bf 11} (1999) 447
[hep-ex/9907002].
%%CITATION = HEP-EX 9907002;%%

%\cite{Breitweg:2000sa}
\bibitem{Breitweg:2000sa}
J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``Search for resonances decaying to e+ jet in e+ p interactions at HERA,''
Eur.\ Phys.\ J.\ C {\bf 16} (2000) 253
[hep-ex/0002038].
%%CITATION = HEP-EX 0002038;%%

%LQ H1
\bibitem{osk-953} 
H1 Collaboration, Abstract {\bf 953}, submitted to ICHEP 2000, Osaka.
%``Search for Leptoquarks in $ep$ collisions at HERA'' 

%LQ ZEUS
\bibitem{osk-1038} 
ZEUS Collaboration, Abstract {\bf 1038}, submitted to ICHEP 2000, Osaka.
%``Search for Leptoquarks in $ep$ collisions at HERA'' 


%LQ e-p H1
\bibitem{osk-954} 
H1 Collaboration, Abstract {\bf 954}, submitted to ICHEP 2000, Osaka.\\
ZEUS Collaboration, Abstract {\bf 552} submitted to EPS HEP 1999, Tampere.
%``A Search for Leptoquark Bosons in $e^-p$ Collisions at HERA'' 

%\cite{Buchmuller:1987zs}
\bibitem{Buchmuller:1987zs}
W.~Buchmuller, R.~Ruckl and D.~Wyler,
%``Leptoquarks in lepton quark collisions,''
Phys.\ Lett.\ B {\bf 191} (1987) 442.
%%CITATION = PHLTA,B191,442;%%
Erratum-ibid.B448:320,1999 

%\cite{Breitweg:2001ks}
\bibitem{Breitweg:2001ks}
J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``A search for resonance decays to anti-nu jet in e+ p scattering at  HERA,''
Phys.\ Rev.\ D {\bf 63} (2001) 052002
[hep-ex/0009059].
%%CITATION = HEP-EX 0009059;%%


%SUSY H1
%Osaka 957
%\cite{Adloff:2001at}
\bibitem{Adloff:2001at}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``Searches at HERA for squarks in R-parity violating supersymmetry,''
hep-ex/0102050.
DESY-01-021, Submitted to Eur.Phys.J.C 
%%CITATION = HEP-EX 0102050;%%

%SUSY ZEUS
\bibitem{osk-1042} 
ZEUS Collaboration, Abstract {\bf 1042}, submitted to ICHEP 2000, Osaka.
%``Search for squark production in R-parity violating interactions at HERA, 

%\cite{Kuhn:1984rj}
\bibitem{Kuhn:1984rj}
J.~Kuhn and P.~Zerwas,
%``Excited Quarks And Leptons,''
Phys.\ Lett.\ B {\bf 147} (1984) 189.
%%CITATION = PHLTA,B147,189;%%

%\cite{Hagiwara:1985wt}
\bibitem{Hagiwara:1985wt}
K.~Hagiwara, D.~Zeppenfeld and S.~Komamiya,
%``Excited Lepton Production At Lep And Hera,''
Z.\ Phys.\ C {\bf 29} (1985) 115.
%%CITATION = ZEPYA,C29,115;%%


%\cite{Adloff:2000gv}
\bibitem{Adloff:2000gv}
C.~Adloff {\it et al.}  [H1 Collaboration],
%``A search for excited fermions at HERA,''
Eur.\ Phys.\ J.\ C {\bf 17} (2000) 567
[hep-ex/0007035].
%%CITATION = HEP-EX 0007035;%%

%f* ZEUS
\bibitem{osk-1040} 
ZEUS Collaboration, Abstract {\bf 1040}, submitted to ICHEP 2000, Osaka.
%``Search for excited fermions in $ep$ collisions at HERA'', 

%excited nu* H1
\bibitem{osk-956} 
H1 Collaboration, Abstract {\bf 956}, submitted to ICHEP 2000, Osaka.
%``A Search for Excited Neutrinos in $e^-p$ Collisions at HERA'',  


%\cite{Adloff:1998aw}
%\bibitem{Adloff:1998aw}
%C.~Adloff {\it et al.}  [H1 Collaboration],
%``Observation of events with an isolated high energy lepton and missing  transverse momentum at HERA,''
%Eur.\ Phys.\ J.\ C {\bf 5} (1998) 575
%[hep-ex/9806009].
%#%CITATION = HEP-EX 9806009;%%

%\cite{Breitweg:2000ie}
%\bibitem{Breitweg:2000ie}
%J.~Breitweg {\it et al.}  [ZEUS Collaboration],
%``W production and the search for events with an isolated high-energy  lepton and missing transverse momentum at HERA,''
%Phys.\ Lett.\ B {\bf 471} (2000) 411
%[hep-ex/9907023].
%#%CITATION = HEP-EX 9907023;%%


%w prod H1
\bibitem{osk-974} 
H1 Collaboration, Abstract {\bf 974}, submitted to ICHEP 2000, Osaka.
%``W production in ep collisions at HERA''

%isol lepton ZEUS
\bibitem{osk-1041} 
H1 Collaboration, Abstract {\bf 1041}, submitted to ICHEP 2000, Osaka.
%``Search for events with isolated high-energy leptons and missing transverse momentum at HERA''

%single top H1
\bibitem{osk-961} 
H1 Collaboration, Abstract {\bf 961}, submitted to ICHEP 2000, Osaka.
%``Search for Single Top Production in $e^{\pm}p$ collisions at HERA, 

\end{thebibliography}