\section{Super-beam experiments}

\subsection{Project in Japan: JHF-Kamioka project}
\hspace*{\parindent}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure}[htbp]
\renewcommand{\baselinestretch}{1}
\begin{center}
\includegraphics[height=4cm]{japan1.eps}
\includegraphics[height=4cm]{nmuintcc_oab.eps}
\end{center}
\vspace{-0.4cm}
\caption{(Left) Locations of JAERI-Tokai site and SK.
(Right) Expected spectrum of CC interactions at SK.
The solid (black), dashed (red) and dotted (blue) histograms are 
OA1.5$^\circ$, OA2$^\circ$ and OA3$^\circ$, respectively. \footnote{Decay pipe length is
80~m although current design is 130~m.}
}
\label{fig:JHFnu-spec}
\vspace{-0.2cm}
\end{figure}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
In Japan, construction of a MW proton accelerator complex, now called as
J-PARC, is going on at JAERI-Tokai site aiming the completion by March,
2007 \cite{J-PARC}.
%
Using the 50~GeV proton synchrotron in J-PARC, a long baseline neutrino
oscillation experiment is being planned. (The 50-GeV related facilities in the
project are 
still called as JHF.) At the first phase of the project, the power of the 50~GeV
PS is 0.75~MW and SK will be used as a far detector. The
intensity of the neutrino beam is expected to be about 2 orders of magnitudes
higher than K2K. Locations of JAERI and SK is shown in Fig.~\ref{fig:JHFnu-spec}.
The baseline length between JAERI and SK is 295 km. In the second phase, we plan
to use upgraded 4-MW PS and 1-Mt ``Hyper-Kamiokande''\cite{hyperk}.

The goals of the first phase are the precision measurements of
oscillation parameters in $\nu_\mu$ disappearance and
discovery of $\nu_e$ appearance. Also, $\nu_\mu\rightarrow \nu_\tau$ or
$\nu_\mu\rightarrow \nu_s$ oscillation can be tested by measuring number of NC
interactions in SK.
%
%
The features of the experiment can be summarized as follows:
\begin{enumerate}
\item Use of low-energy narrow-spectrum neutrino beam tuned at oscillation
 maximum in order to maximize the sensitivity. The
 baseline length of 295~km corresponds to the oscillation 
maximum of $E_\nu\simeq 700$~MeV when $\Delta m^2 = 3\times 10^{-3}$~eV$^2$.
\item Use of ``off-axis''(OA) configuration to produce the highest possible
intensity with a narrow energy spread \cite{OAB}. To adjust the peak of the neutrino
spectrum at oscillation maximum, the OA angle will be at $2\sim 3$ degree.
\item Use of gigantic water \Cer detector (SK) as a far detector. SK
   has excellent performance in detecting low-energy neutrinos.
\item  Neutrino energy of each event is reconstructed from momentum of a
 charged lepton in charged current quasi elastic (CCqe) interaction, $\nu_l +
n\rightarrow l^- + p$. The energy resolution in this method is as good as
$\sim 80$~MeV. Since the CCqe reaction dominates in the sub-GeV region,
efficient and clean measurement of neutrino energy spectrum is possible.
\end{enumerate}
%

Technical design of the neutrino facility is in progress \cite{Ichi}.
%
%The intensity of the PS is $3.3\times 10^{14}$ proton/pulse,
%acceleration cycle is 3.6~s.
%The extracted proton beam is bent about 90$^\circ$ toward the SK direction by
%super-conducting magnets and hit a production target.
%Current design of the target is typically 3-cm diameter and 1-m long Carbon rod.
%The produced pions are focused by 3 electromagnetic horns operated at 320~kA.
%The length of the decay pipe is 130~m measured from the target.
%
Expected numbers of interactions at SK with 2$^\circ$ OA are about 4500 (3000)
for total (CC) interactions in fiducial volume of 22.5~kt in 1 year.
%Typical 1 year operation is defined as $10^{21}$ protons on target (POT).
The expected $\nu_\mu$ spectrum at SK without oscillation is plotted in
Fig.~\ref{fig:JHFnu-spec}. One of the critical issue in searching for $\nu_e$
appearance is intrinsic $\nu_e$ contamination in the beam which comes from
$\mu$ and K decay. The $\nu_e$ to $\nu_\mu$ flux ratio is as small as 0.2\% at
the  peak energy of $\nu_\mu$ spectrum.
%This indicate that, by combining with the high-resolution energy reconstruction
%with CCqe, high sensitivity $\nu_e$ appearance search becomes possible.

In order to monitor the neutrino beam and to predict the flux and spectrum at SK
as precisely as possible, muon monitor behind the beam dump and front neutrino
detector at 280~m from the production target will be installed.
In addition, possibility of placing a neutrino detector at $\gtrsim 1.5$~km from
the target is being seriously discussed. At these distances, neutrino spectrum
becomes almost identical to that at SK. This could eliminate one of the largest
systematic uncertainties in LBL experiments, i.e., spectrum difference between
far and near site.

\subsection{Projects in US}
%%%%%%%%%%%%%%%%%%%%%%%
% FNAL
%%%%%%%%%%%%%%%%%%%%%%%
\hspace*{\parindent}In US, the MINOS experiment is now under construction, in
which $\nu_\mu$ beam is produced by the proton beam from Main Injector (MI) at
FNAL and detected by a detector which is being constructed in Soudan mine, 730km
from FNAL. The proton beam intensity from MI is 0.4MW.
%
Recently, possibilities to upgrade the power of the beam \cite{FNAL-Driver} and
to construct an 
``off-axis'' detector \cite{OA-NuMI} are being seriously discussed to conduct
next-generation high-sensitivity LBL experiments.

The intensity upgrade is an idea to replace the current 8-GeV booster
by a rapid-cycling high-intensity 16-GeV synchrotron. It increases
intensity in the MI by a factor of four, i.e. to 1.6~MW \cite{FNAL-Driver}.
In the long term, upgrade to 4~MW is also envisaged by adding
a 600~MeV linac and a 3~GeV pre-booster.
Improvement in the precision of NuMI experiment is expected by the upgrade.

New OA detector(s) are proposed to exploit the full potential of the NuMI
neutrino beam and  to complement the MINOS experiment \cite{OA-NuMI}.
The main goal of the proposal in the first phase is to search for $\nu_e$
appearance with a detector of the order of 20-kt fiducial mass.
In the second phase, with the increased beam intensity by the
Proton Driver and increase of the detector mass by about factor of five,
higher sensitivity search of $\nu_e$ appearance or a measurement of CP 
violation would be possible.

The expected spectra at off axes are shown in Fig.~\ref{fig:OA-NuMI}.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure}[htbp!]
\centerline{\includegraphics[width=10cm]{oanumi-flux.eps}}
\vspace{-0.3cm}
\caption{Energy spectra of CC events expected at a far detector location 735km
from FNAL at various OA angles for the NuMI low-energy beam setting (left)
and the medium-energy setting (right) \cite{OA-NuMI}.\label{fig:OA-NuMI}}
\vspace{-0.2cm}
\end{figure}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
The possible sites for the detector is being investigated.
The distances from FNAL to the candidate sites ranges from 600 to 900~km.
%Several types of detectors are now under consideration.
Low-Z tracking calorimeter is mainly being studied as a far detector while
the other options, water-Cherenkov or liq. Ar TPC are
still kept. In order to achieve good electron identification, 
sampling frequency of $1/4\sim 1/3$ $X_0$ (radiation length)
is being discussed in the case of the tracking calorimeter.
The expected energy resolution is estimated to be about 16\% for the energy
range $1\sim 3$~GeV by Monte-Carlo simulation assuming $1/3 X_0$ sampling.


%%%%%%%%%%%%%%%%%%%%%%%
% BNL
%%%%%%%%%%%%%%%%%%%%%%%
There is another interest to conduct a (very) long baseline experiment using a
proposed beam from BNL \cite{BNL-VLBL}.
The neutrino beam is produced by 28~GeV proton beam from Alternating Gradient
Synchrotron (AGS) at BNL and is detected by huge water Cherenkov detector
of 500~kt or more at more than 2000~km.
The primary purposes are precise determination of oscillation parameters, search
for $\nu_e$ appearance and CP violation.
This idea consists of
(1) Intensity upgrade of AGS from 0.14~MW to 1~MW,
(2) Construction of new neutrino beam line
(3) Construction of underground water Cherenkov detector of 0.5Mt fiducial mass.
The locations of BNL and possible detector sites and expected neutrino 
spectra are shown in Fig.~\ref{fig:BNL}.

%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure}
  \begin{center}
%    \includegraphics*[width=0.9\textwidth]{figs/bnl_near.eps}
    \includegraphics*[width=6cm]{bnl_wipp_lead.eps}
    \includegraphics*[width=4.5cm]{dm20025.eps}
\vspace{-0.3cm}
    \caption
    {(Left) Locations of BNL and possible detector sites
      Homestake and WIPP at 2540 and 2880 km from BNL, respectively.
      (Right) Expected spectrum of detected  events in a 0.5 MT detector at
      2540 km from BNL including quasielastic signal and CC-single pion 
background with 1.0 MW of beam power in 5 years of running.
The top histogram is without oscillations;
the middle error bars are with oscillations and the bottom histogram is
the contribution of the background to the oscillated signal only.  
 This plot is for $\mdmatm =
      0.0025~\meV^2$.
%      The error bars correspond to the statistical error expected in
%      the bin. A 10 \% detector energy resolution is assumed.
%        At low energies the Fermi movement, which is included in 
%simulation, will dominate the resolution \cite{BNL-VLBL}.
 \label{fig:BNL}}
    \label{blines}
  \end{center}
\vspace{-0.5cm}
\end{figure}

\subsection{Projects in Europe}
\hspace*{\parindent} In Europe, there is an idea of superbeam LBL experiment in
which the neutrino beam is produced by Super Proton Linac (SPL) 
and detected by a detector at Modane laboratory in Furejus tunnel, 130~km
from CERN ~\cite{CERN-SB}. The proposed SPL is a 2.2 GeV linac with 4 MW beam power
operated at 75-Hz repetition rate and $1.5\times 10^{14}$ protons/pulse.
The neutrino beam is a conventional wide-band beam and the expected neutrino
spectrum at the detector site is plotted in Fig.~\ref{fig:CERN-flux}.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure}[htbp!]
\centerline{\includegraphics[width=10cm]{CERN-flux.eps}}
\vspace{-0.3cm}
\caption{Spectrum of neutrino beam from CERN SPL.\label{fig:CERN-flux}}
\end{figure}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
The expected neutrino spectrum ranges $\lesssim 500$~MeV which
matches with with the oscillation maximum of $\sim 300$~MeV
at $\Delta m^2 = 3\times 10^{-3}$~eV$^2$.
Currently two types of detector technology are under consideration,
i.e., water Cherenkov detector of SK type and liquid scintillater detector
of LSND/MiniBooNE type. The detector fiducial mass is supposed to be 40~kt.


\subsection{Summary of experiments}
\hspace*{\parindent}
Current and planned (superbeam) LBL experiments are summarized in
Table~\ref{tbl:SumExp}.
As can be seen in the $L/L_{\rm osci}$ column, neutrino energy and the baseline
length in most of the superbeam experiments are chosen so that the neutrino
energy matches at the oscillation maximum.
Expected number of interactions in the superbeam experiments is more than 2 order of
magnitude higher than current on-going experiment, K2K.
\begin{table}[htbp!]
\caption{Summary of (super)beam LBL experiments. The column ``FM'' is the
  fiducial mass of far detector. The letters in ``status''
  column mean ``A'': accelerator, ``B'': neutrino beam line, ``D'': far
  detector, and the meaning of the symbols are $\circledcirc$: in operation,
$\bigcirc$: construction, $\vartriangle$: design. \label{tbl:SumExp}}
\vspace{-0.5cm}
\begin{center}
\small
\begin{tabular}{lcccccccccc}
\hline\hline
             & $E_p$ & Power & $E_\nu$ & $L$ & $L/L_{\rm osci}$ & FM  & \#CCint
             & \multicolumn{3}{c}{status} \\
             & (GeV) & (MW)  & (GeV)   & (km)&                  &(kt) & (/yr) &
             A & B & D\\
\hline
K2K          &  12   & 0.005 &  1.3    & 250 &      0.47        & 22.5&    30 &
             \multicolumn{3}{c}{running} \\
MINOS        & 120   & 0.4   &  3.5    & 730 &      0.51        & 5.4 & 2.5k  &
             \multicolumn{3}{c}{start 2005}\\ 
{\tiny ICARUS/OPERA} & 400   & 0.3   & 17 & 732 &  0.10 & {\tiny
             2.35/1.65}&{\tiny 6.5k/4.6k}& \multicolumn{3}{c}{start 2006} \\
JHF$\nu$     &  50   & 0.75  &  0.7    & 295 &      1.02        & 22.5&    3k &
             $\bigcirc$ & $\vartriangle$  & $\circledcirc$\\
OA-NuMI      & 120   & 0.4   &  2.0    & 700 &      0.89        & 20  &  2.4k &
             $\circledcirc$ & $\bigcirc$ & $\vartriangle$\\
JHF$\nu$II   &  50   & 4.0   &  0.7    & 295 &      1.02        & 540 &  480k &
             $\vartriangle$ & $\vartriangle$ & $\vartriangle$\\
Super-AGS    &  28   & 1.3   &  1.5    & 2540&       4.1        & 500 &   16k &
             $\vartriangle$ & $\vartriangle$ & $\vartriangle$\\
SPL-Furejus  & 2.2   & 4.0   &  0.26   & 130 &      1.21        & 40  &  650 &
             $\vartriangle$ & $\vartriangle$ & $\vartriangle$\\
\hline\hline
\end{tabular}
\end{center}
\small
$^{*1}$ : The definition of neutrino oscillation length is 
$L_{osci.}= \frac{\pi}{2} \cdot \frac{<E_\nu>}{1.27 \Delta \rm m^2}$ for 
$\Delta \rm m^2 = 3 \times 10^{-3}$~$\rm eV^2$.\\
\end{table}
\normalsize
%
