LATEST CHORUS AND NOMAD RESULTS
K. Zuber
The final result of the NOMAD searches on \nmu - \ntau oscillations as well as the current status of CHORUS are described. The \nmune analysis of \no excludes the parameter region of LSND in the range \delm $>10$ \evs. New results on charm physics from both experiments are presented.
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\newcommand{\evs}{\mbox{eV$^2$} } 
\newcommand{\bnel}{\mbox{$\bar{\nu}_e$} }    
\newcommand{\bnmu}{\mbox{$\bar{\nu}_\mu$} }    
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\begin{document}
\vspace*{4cm}
\title{LATEST CHORUS AND NOMAD RESULTS}

\author{ K. Zuber }

\address{Department of Physics, University of Oxford, Keble Road,\\
Oxford OX1 3RH, England}

\maketitle\abstracts{
The final result of the NOMAD searches on \nmu - \ntau oscillations as well as the current status of 
CHORUS are described. The \nmune analysis of \no excludes 
the parameter region of LSND in the range \delm $>10$ \evs. New 
results on charm physics from both experiments are presented.}

\section{Introduction}
A non-vanishing rest mass ot the \neu has far reaching consequences from cosmology down to particle 
physics. For a recent review see \cite{kai}. 
In the last years growing evidence for such a mass arose in \neu \osz \exps .  
In a simple two flavour mixing scheme the \osz probability $P$ is given by
\be  
P (L/E_\nu) = \sint{} \sin^2(1.27 \delm_{ij} L/E_\nu)  
\ee  
with $\Delta m^2_{ij}$ = $\mid m_j^2 -m_i^2 \mid$, $\theta$ as the mixing angle, L the
source-detector distance and \enu the 
\neu energy. Short baseline experiments with high energy neutrino beams offer the chance
to probe small mixing angles at rather larger \delm (\delm $>$ 1 \evs). It was the intension of
\ch and \no to probe \sint almost down to about $10^{-4}$ for \nmuntau oscillations 
in that region. High statistics $\nu$N scattering allows also for various other kinds of
studies,
among them charm physics.

\section{The experiments}
\label{subsec:prod} 
Both experiments were performed in the West Area Neutrino Facility (WANF)
at CERN during the years 1994-1998. The beam was an almost pure \nmu beam with small contaminations of \bnmu
($\approx$ 6 \%) and \nel ($\approx$ 1 \%).  
The active target of \ch consisted of nuclear emulsions with a total mass of 770
kg \cite{chorus}. 
%The main advantage is the excellent spatial resolution of emulsions of a few $\mu$m. 
For timing purposes and for extrapolating the tracks back into the emulsions, a scintillating fibre tracker was
interleaved.
% consisting of 500 $\mu$m diameter fibres of 2.3 m length. 
Behind the target complex followed a hexagonal spectrometer
magnet for
momentum measurement, a high resolution spaghetti calorimeter for measuring hadronic showers and a muon spectrometer.
The scanning of the emulsions is performed with high-speed CCD microscopes.\\
\no was using drift chambers as target and tracking medium \cite{nomad}.
%, with the chamber
%walls as interaction targets and the chambers for precise particle tracking. 
In total there were 44 chambers located in a 0.4 T magnetic field with a fiducial mass of 2.7 tons.
They were followed by a transition radiation detector (TRD) for e/$\pi$ separation,
further electron identification devices in form of a preshower detector
and an electromagnetic lead glass calorimeter. 
A hadronic calorimeter 
%in form of an iron-scintillator sampling calorimeter 
and a set of 10 drift chambers for muon identification followed. 
%The detector was located within a magnetic field of 0.4 T, perpendicular to the beam
%axis for momentum determination. 
In front of the drift chambers another iron-scintillator calorimeter of about 20 t target mass was
installed. 
%For more detailed descriptions of the experiments
%see \cite{chorus,nomad}.

\section{\nmuntau and \nentau analysis}
%Both experiments were complementary in the way of their $\tau$-detection technique.
The analysis obtained by \ch is based on the search of a kink, coming from the decay of the $\tau$-lepton.
%, which is producing
%a short track a few 100 $\mu$m. 
%The decay product, a negative muon or negative charged hadron can then be observed
%as being displaced from the primary vertex. 
The
data set are divided in 1$\mu$ and 0$\mu$ samples based on the possible observation of a muon in the spectrometer. To
reduce the load for scanning, further cuts on momentum and angles with respect to the beam are applied. 
%The 1$\mu$ sample should contain only one negative track with 
%momentum less than 30 GeV, the 0$\mu$ sample should at least have one negative track in the interval 1-20
%GeV. Additionaly the negative tracks should have an angle with respect to the beam of 0.05 $ < \theta <
%0.4$ rad. 
The event finding proceeds in three steps: a vertex location in the emulsion, the search for the
decay kink and at the end an eye-scan of candidates. The main background arises from charm production.
%, which
%can be significantly reduced by implying a cut on the transverse momentum $p_T >$ 250 MeV and by using the
%maximum length of the decay path. 
\ch observed 0 events in the 1$\mu$ (0.1 expected)
and 4 events in the 0$\mu$ sample (3.3 expected). This can be transformed into an upper limit on
the \osz probability of P(\nmuntau) $< 3.4 \cdot 10^{-4}$ (90 \% CL) \cite{chnutau}. With a new, more effective scanning
method the
analysis will be repeated.\\
\no is not able to observe the $\tau$-lepton directly but relies on the decay kinematics. The variables
of use here are basically imbalance and isolation. 
%\nmu CC events are characterised by the fact that the
%outgoing muon is in the transverse plane back to back with the hadronic final state and only a small value
%of missing $p_T$ is expected. On the other hand NC events have a rather large missing $p_T$ but in principle
%no well isolated charged track. The signal of \ntau CC is somewhere in between. 
To obtain maximum sensitivity for an oscillation signal all degree of freedoms of the kinematics and their
correlations have to be exploited. In this way the $\tau \ra e$ and $\tau \ra h(n \pi^0), 3h(n\pi^0)$ decay
modes were explored, separated in a low multiplicity and deep inelastic sample. 
%To account for the above
%requirements of using adequate kinematic variables and their correlations, 
A maximum likelihood method was used
together with a blind-box analysis. The box itself is split
into bins, where most of the sensitivity is related to low background bins. 
In these bins 1.60$^{+1.69}_{-.39}$ background events were expected and 1 event was observed. The final result from the
analysis is a limit of P(\nmuntau) $< 1.68 \cdot 10^{-4}$ (90 \% CL) \cite{nonutau}.\\
Both experiments took advantage of the fact, that there is a 1\% beam contamination of $\nu_e$. Correcting for
the higher average energy of the \nel component and modified acceptances, they were able to give
limits also on \nentau oscillation probabilities as P(\nentau) $< 2.6 \cdot 10^{-2}$ (\ch ) and P(\nentau) $< 1.68 \cdot
10^{-2}$ (\no ) respectively. The current status is shown in Fig.~\ref{fig:osci}.

\begin{center}
\begin{figure}[ht]
%\rule{5cm}{0.2mm}\hfill\rule{5cm}{0.2mm} 
\hskip 2cm
%\rule{5cm}{0.2mm}\hfill\rule{5cm}{0.2mm} 
%\begin{tabular}{cc}
\epsfig{figure=sin2m2_final.eps,width=5.5cm,height=5.5cm} 
\hskip 1cm
\epsfig{figure=sin2m2e_final.eps,width=5.5cm,height=5.5cm} 
%\end{tabular}
\caption{Current status of \nmuntau (left) and \nentau (right) oscillation searches obtained by \ch and \no.
Superimposed are results from other experiments \label{fig:osci}}  
\end{figure}  
\end{center}

\section{\nmune analysis}
%no is also able to perform a \nmune analysis, exploring a large fraction of the LSND-evidence \cite{lsnd}.
A \nmune signal would manifest itself in \no as an increase of \nel CC events. The difference in the energy and radial
distributions of incident \nel and \nmu lead to an enhancement of \nel CC events at low \nel energies and small radii
with respect to
the beam
axis. To reduce systematic effects the ratio $R_{e\mu}$ defined as
\be
R_{e\mu} = \frac{'' \nel CC''}{'' \nmu CC''} (\enu, r) 
= \frac{e^- (\nel CC) + e^- (bkg) + e^- (\nel^{osc} CC)}{\mu^- (\nmu CC) + \mu^- (bkg)} (\enu, r) 
\ee
is investigated.
The sensitivity can be enhanced to explore $R_{e\mu}$ as a function of neutrino energy \enu and
the radial position of the neutrino interaction vertex $r$. The analysis is also based on kinematical 
criteria and performed as a ''blind'' analysis.  The crucial part and main uncertainty is a robust
prediction of the neutrino flux and energy spectrum.
% Using detailed beam simulations and the observed \nmu, \bnmu and 
%\bnel CC events, the various contributions of pions and kaons can be disentangled and an accurate
%prediction for the \nel flux, produced dominantly by $K^+$ with an 18 \% contribution of $K_L$ can be made.
No oscillations were observed \cite{slava} resulting in a value of \delm $>$ 0.4 \evs for maximal mixing and
\sint $< 1.2 \cdot 10^{-3}$ for large $\Delta m^2$. \no excludes the LSND evidence\cite{lsnd} for \delm
$>$ 10 \evs. 
The $R_{e\mu}$ ratio and the resulting exclusion plot
are shown in Fig.~\ref{fig:nmune}.

\begin{figure}[hb]
%\rule{5cm}{0.2mm}\hfill\rule{5cm}{0.2mm}  
\hskip 2cm
%\rule{5cm}{0.2mm}\hfill\rule{5cm}{0.2mm} 
\epsfig{figure=ratio_talk1.eps,width=5cm,height=5cm} 
\hskip 1cm
\epsfig{figure=numunue2001.eps,width=5cm,height=5cm} 
\caption{Left: $R_{e\mu}$ as a function of visible energy. The points show the \no data, the histogram
corresponds to the expected Monte Carlo predictions assuming no oscillations and 1$\sigma$ systematic errors
added in quadrature. Right: 90 \% CL exclusion region in the \delm - \sint plot and the sensitivity of the
\no analysis superimposed on the results of other experiments. A new KARMEN analysis\protect \cite{karmen} and a
combined
LSND-KARMEN analysis\protect \cite{klaus} exist.
\label{fig:nmune}}  
\end{figure} 

\section{Charm physics} 
%Neutrino nucleon scattering also provides important contribution to charm physics.  
Charm can be produced via charged current interactions on d- and s-quarks in the nucleon, therefore allowing to explore
their structure functions in the nucleon, especially s(x). 
%Additionaly the coupling is associated with the CKM-matrix elements $\mid V_{cd}^2 \mid$ and $\mid
%V_{cs}^2 \mid$. 
The charm fragmention can be explored by measuring the various charmed mesons in the final state. 
%Dimuon production given by 
%\begin{eqnarray} \nu _\mu \;+\;{\rm N}\;\longrightarrow \;\mu ^{-}\!\! &+&\!c\;+\;{\rm
%X} \\ &&\!\!\hookrightarrow s\;+\;\mu ^{+}\;+\;\nu _\mu \nonumber 
%\end{eqnarray} 
%is well suited for determining the
%charm quark mass and the structure function s(x). The differential cross section for dimuon production is expressed
%generally as 
%\begin{equation} {\frac{d^3\sigma (\nu _\mu N\rightarrow \mu ^{-}\mu ^{+}X)}{d\xi \ dy\ dz}}=
%{\frac{d^2\sigma (\nu _\mu N\rightarrow cX)}{d\xi \ dy}\ }D(z)\ B_c(c\rightarrow \mu ^{+}X), \label{eq:dimuon}
%\end{equation} 
%where $\xi = x (1 + \frac{m_c^2}{Q^2})$ is the slow rescaling variable, $D(z)$ describes the hadronization of charmed
%quarks and $B_c$ is the weighted average
%of the semi-leptonic branching ratios of the charmed hadrons. By measuring
From the ratio of opposite sign dimuons versus single muon production as a function of \enu,
$m_c$ can be determined from the threshold behaviour. Such an analysis\cite{noosdm} was performed by \no using 
15 \% of the data set (Fig.~\ref{fig:charm}). 
%Because both experiments have excellent tracking possibilities als a search for charmed mesons in the final state can
%be performed.
Recently \ch performed a search for \dnull production \cite{chdo}. In total 283 candidates are observed, with an
expected
background of 9.2 events coming from K and $\Lambda$ decay. The ratio $\sigma(\dnull)/\sigma(\nmu CC)$
is found to be $(1.99 \pm 0.13(stat.)\pm0.17(syst.))\cdot 10^{-2}$ at 27 GeV average \nmu energy
(Fig.~\ref{fig:charm}).
%The ratio of cross sections as a function of \enu is shown in Fig.~\ref{fig:charm}.
NOMAD performed a search for \ds -production using the decay chain $\ds \ra \dnull + \pi^+$
followed by 
$\dnull \ra K^- + \pi^+$. In total 35 $\pm$ 7.2 events could be observed resulting in a \ds yield in \nmu CC
interactions of
(0.79$\pm$0.17(stat.)$\pm$0.10(syst.)) \% \cite{nodstar}.

\begin{figure} 
%\rule{5cm}{0.2mm}\hfill\rule{5cm}{0.2mm} 
\hskip 2cm
%\rule{5cm}{0.2mm}\hfill\rule{5cm}{0.2mm} 
\epsfig{figure=dimmcrate.eps,width=5.cm,height=5.5cm}
\hskip 1cm
\epsfig{figure=chorus_do.ps,width=5.5cm,height=5.5cm} 
\caption{Left: $\sigma(\mu^+\mu^-)/\sigma(\nmu CC)$ as a function of \enu for
a charm quark mass of $m_c = 1.3 GeV/c^2$. Also shown are the CCFR
(open circles) and CDHS data (crosses). The theoretical curve is using the slow rescaling model in LO
QCD, a charm quark mass of $m_c = 1.3 GeV/c^2$, a strange quark suppression of $\kappa = 0.48$, an average semileptonic
branching ratio of 0.095 and the validity of the CCFR structure functions.
Right:  \dnull production rate as a function of \enu as obtained by \ch. The result of this analysis are shown as solid
lines and
compared with those of the E531 experiment, scaled appropriately (dashed lines). 
%The data points of E531 have been
%scaled with their
%measurement of the \dnull rate compared to the total charm production rate. 
The curve shows a fit based on the slow
rescaling model to NOMAD charm data multiplied by the (\dnull/charm) cross-section ratio measured.
\label{fig:charm}} 
\end{figure}

\section{Summary}
Both recent short baseline experiments at CERN, \ch and \no, boosted the limit on the mixing angle
\sint for \delm $>$ 10 \evs by an order of magnitude and more with respect to former experiments.
The improvement was obtained in the \nmuntau and \nentau channel as well. A recent \no analysis in the
\nmune channel can exclude the parameters of the LSND evidence for \delm $>$ 10 \evs. Several interesting
results on charm physics were already obtained and can be expected in the future.

\section*{Acknowledgments}
This work is supported by a Heisenberg Fellowship of the Deutsche Forschungsgemeinschaft. I would
like to thank my collegues from \ch and \no for valuable discussions.

\section*{References}
\begin{thebibliography}{99}
\bibitem{kai} K. Zuber, \Journal{\PRP}{305}{295}{1998}  
%\bibitem{samoil}S. M. Bilenky, C. Giunti, W. Grimus, \Journal{\PNPP}{43}{1}{1999} 
%\bibitem{wanf} L. Casagrande {\it et al}, CERN-96-06
\bibitem{chorus}E. Eskut {\it et al}, \Journal{\NIMA}{401}{7}{1997}
\bibitem{nomad} J. Altegoer {\it et al}, \Journal{\NIMA}{404}{96}{1998}
\bibitem{chnutau}E. Eskut  {\it et al}, \Journal{\PLB}{497}{8}{2001}
\bibitem{nonutau}  P. Astier  {\it et al}, \Journal{\NPB}{611}{3}{2001}
\bibitem{slava} V. Valuev, Proc. Int. Europhysics Conf. on High Energy Physics, Budapest 2001
\bibitem{lsnd} A. Aguilar  {\it et al}, \Journal{\PRD}{64}{112007}{2001}
\bibitem{karmen} B. Armbruster {\it et al}, hep-ex/0203021
\bibitem{klaus} E. D. Church {\it et al}, hep-ex/0203023
\bibitem{noosdm} P. Astier {\it et al}, \Journal{\PLB}{486}{35}{2000}
\bibitem{chdo} A. Kayis-Topasku {\it et al}, \Journal{\PLB}{527}{173}{2002}
\bibitem{nodstar}  P. Astier {\it et al}, \Journal{\PLB}{526}{278}{2002}

\end{thebibliography}

\end{document}

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hep-ex0206006.extracted_bib
\begin{thebibliography}{99}
\bibitem{kai} K. Zuber, \Journal{\PRP}{305}{295}{1998}  
%\bibitem{samoil}S. M. Bilenky, C. Giunti, W. Grimus, \Journal{\PNPP}{43}{1}{1999} 
%\bibitem{wanf} L. Casagrande {\it et al}, CERN-96-06
\bibitem{chorus}E. Eskut {\it et al}, \Journal{\NIMA}{401}{7}{1997}
\bibitem{nomad} J. Altegoer {\it et al}, \Journal{\NIMA}{404}{96}{1998}
\bibitem{chnutau}E. Eskut  {\it et al}, \Journal{\PLB}{497}{8}{2001}
\bibitem{nonutau}  P. Astier  {\it et al}, \Journal{\NPB}{611}{3}{2001}
\bibitem{slava} V. Valuev, Proc. Int. Europhysics Conf. on High Energy Physics, Budapest 2001
\bibitem{lsnd} A. Aguilar  {\it et al}, \Journal{\PRD}{64}{112007}{2001}
\bibitem{karmen} B. Armbruster {\it et al}, hep-ex/0203021
\bibitem{klaus} E. D. Church {\it et al}, hep-ex/0203023
\bibitem{noosdm} P. Astier {\it et al}, \Journal{\PLB}{486}{35}{2000}
\bibitem{chdo} A. Kayis-Topasku {\it et al}, \Journal{\PLB}{527}{173}{2002}
\bibitem{nodstar}  P. Astier {\it et al}, \Journal{\PLB}{526}{278}{2002}

\end{thebibliography}