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\begin{document} 
 
\BookTitle{\itshape The 28th International Cosmic Ray Conference} 
\CopyRight{\copyright 2003 by Universal Academy Press, Inc.} 
%\tableofcontents 
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\chapter{%   %%%%%%%%% <===== TITLE of the contribution 
%%%%%%%%%%% The first letter of each word should be capital letter.
The IceCube High Energy Neutrino Telescope}

\author{%
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% the title/author information fits within 1 page.
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S.~Yoshida$^{1}$ for the IceCube Collaboration$^2$\\ 
{\it(1) Dept. of Physics, Chiba University, Chiba 263-8522 Japan\\
   (2) The full author list is found in Ref.[4]}\\
}%% end of author


\section*{Abstract}
         The IceCube Neutrino Telescope, a huge Neutrino Telescope
with 1 cubic km instrumented volume, starts construction
in 2004. The project status and the expected sensitivity 
and performance for detecting high energy cosmic neutrinos are reported. 
%Preliminary results based on AMANDA experience without taking into account 
%IceCube's new digital technology indicate  a sensitivity to a diffuse muon
%neutrino energy flux of $10^{-8}$ GeV/cm$^2$ sr sec.
%Proposed models for GRB emission should be observable in less than
%one year.

\section{Introduction: IceCube Detector}

It has been discussed that many of the proposed astrophysical models of ultra-high energy (UHE)
neutrino production would require a scale of a cubic kilometer
target volume to secure their detection. The IceCube detector has been designed
and will be constructed following this philosophy. 
It is the result of further technological development of the
basic ideas of the AMANDA telescope~[1], which has demonstrated the deep
ice at the Soth Pole indeed provides an excellent interaction target 
for UHE neutrino detection,
which validated the idea of having a much larger neutrino telescope
in Antarctica. It will be realized as the IceCube detector~[2].

%=======================================================================
\begin{figure}[t]
  \begin{center}
    \includegraphics[width=0.6\textwidth,clip=true]{icecube-layout.4.eps}
  \end{center}
  \vspace{-1.5pc}
  \caption{Schematic top view of the string arrangement of the IceCube detector
	at the South Pole station.}
\label{fig:icecube_view}
\end{figure}
%=======================================================================

The configuration of the IceCube detector is shown in Fig.~\ref{fig:icecube_view}
The instrumented volume where Cherenkov lights from neutrino-induced
charged leptons is detected contains an array of 4800 PMTs
each enclosed in a transparent pressure sphere to comprise a
Digital Optical module (DOM). Eighty strings are regularly spaced by
125 m over an area of approximately one square kilometer with DOMs
at depths of 1.4 to 2.4 km below the ice surface. Each string,
containing 60 DOMs spaced by 17m, will be deployed into a hole drilled with
pressurized hot water. A complimentary air shower array on the ice surface
is described separately~[3] 

%=======================================================================
\begin{figure}[t]
  \begin{center}
    \includegraphics[width=0.4\textwidth,clip=true]{DOM.ps}
  \end{center}
  \vspace{-1.5pc}
  \caption{Schematic view of the IceCube Digital Optical Module.}
\label{fig:DOM}
\end{figure}
%=======================================================================

The IceCube DOM is shown in Fig.~\ref{fig:DOM} It contains a 10 inch diameter PMT
supported by coupling gel, a signal processing electronics
board, an LED flasher board for calibration, and the PMT base with high voltage
supplier, all of which are housed in the spherical pressure glass.
It contains its own processor, memory flash file system, and real-time
operating system. Its new digital technology enables it to schedule
background communication while acquiring data, to invoke all calibration
functions under software control, and most notably,
to digitize the PMT pulse and store the full waveform information. 

Our current PMT choice is the HAMAMATSU R7081 with 10 dynodes
which has exhibited excellent charge resolution and low noise.
The operation gain is planned to be $\sim 5\times 10^7$
with dynamic range of $\sim 200$ photo-electrons per 15 ns.
The overall noise for each individual DOM is 
targeted to be 500 Hz which can be
realized due to the sterile and low temperature environment
of the deep ice and an effort to use low activity materials. 


\section{Analysis Chain and the Basic Performance}

The backgrounds for searches for extraterrestrial neutrinos
come from atmospheric muons and neutrinos produced
by decay of mesons generated from cosmic ray (CR)
interactions in the atmosphere.
CR-interactions induced background events can be identified
by the fact that they result mainly in down-going tracks
in the instrumented volume of ice. 
Our search for cosmic neutrinos will be performed, therefore,
by excluding the vast backgrounds caused by atmospheric muons
(and eventually atmospheric neutrinos also), which requires extensive simulations.
The main sequence of the simulation and the analysis
procedures are:

{\small
\begin{enumerate}

\item Neutrino and muon generation in the atmosphere by CR
is simulated by the full Monte Carlo Package. 
Astrophysical UHE neutrinos are assumed to follow an $E_{\nu}^{-2}$ energy spectrum
as a benchmark.

\item Propagation of neutrinos and induced muons in the earth
is simulated. 
These simulations give the intensity of neutrinos and muons
%originated in astrophysical sources and the atomospharic CR interactions
entering into our detector volume after propagation through the earth.

\item The Cherenkov light generation and propagation in the deep ice,
taking account of scattering and absorption, is simulated. 
Then the detector response of the PMT array
is modeled by the detector simulation. 
Initially~[4] We used the software package primarily for AMANDA for this purpose.

\item The triggered events are filtered and reconstructed. 

\end{enumerate}
}

Here we only report on the case of $\nu_{\mu}$ inducing high energy muons
since their long range results in a larger detection volume than do the other
charged leptons. Note that the complete reconstruction technique
is based on the AMANDA experience, which implies that the results
are reliable, but also conservative as we did not use the full pulse
shape information available by the IceCube DOMs which will
improve the sensitivity\footnote{The reconstruction used here relies
only on the information carried by the first photon arriving at
the PMT assuming the original AMANDA read-out system.}.

The discrimination of the astrophysical neutrino signals
from the background is based on the geometrical parameters
obtained by the various reconstruction algorithms, the reduced
likelihood of the reconstruction, number of PMT channels
receiving an unscattered Cherenkov photon, the track length
and so on. The details are found in~[4]. The initial
results indicated that the atmospheric muon background 
can be reduced by more than factor of $\sim 10^6$. The atmospheric
neutrino background remains significant, but
applying a channel multiplicity cut can exclude
the background completely since the energy spectrum
of astrophysical neutrinos ($\sim E^{-2}$) is much harder
than that of the background neutrinos ($\sim E^{-3.7}$). 
The effective
area for upward moving neutrino-induced UHE muons is 1.2 km$^2$
at 1 PeV. The pointing resolution is better than 1.0$^{\circ}$.

\section{Sensitivity to Astrophysical $\nu_{\mu}$}

%=======================================================================
\begin{figure}[t]
  \begin{center}
    \includegraphics[width=0.6\textwidth,clip=true]{diffuse.int.eps}
  \end{center}
  \vspace{-1.5pc}
  \caption{Expected sensitivity of the IceCube detector.The various
neutrino production models in AGNs/GRBs are shown for comparison~[5-8].
The {\it mrf} implies the ``Model Rejection Factor'' which is described
in~[4] for details.}
\label{fig:expected_sensitivity}
\end{figure}
%=======================================================================

The sensitivity obtained for a diffuse neutrino flux
is summarized in Fig.~\ref{fig:expected_sensitivity}
$E_{\nu}^2 dN_{\nu}/dE_{\nu} = 1\times 10^{-8}$ cm$^{-2}$ sec$^{-1}$ sr$^{-1}$ GeV
is detectable in five years of observation. The GRB flux appears to be below
the IceCube sensitivity, but coincident search in direction and burst timing
leads to 5$\sigma$ detection of the GRB neutrinos with 200 observed bursts
which can be achieved in less than 1 year detector operation. An angular search
cone of $1^{\circ}$ would constrain models of point sources to those that produce
flux less than $E_{\nu}^2 dN_{\nu}/dE_{\nu} = 2\times 10^{-8}$ cm$^{-2}$ sec$^{-1}$ GeV.

\section{Project Status}

The project has been approved by the U.S. National Science Board
and its total cost noted in the U.S. president's FY2004 budget request
for the NSF, the source of the major fraction of the cost.
Full construction
will start in FY 2004 and take 6 years to complete. 
In this year, defined by project year 2,
production and testing of 150 DOMs are scheduled
in addition to shipping the new hot water drill to the South Pole.
The detector verification, related software to
utilize fully the DOM waveform information, and the efforts
to expand the energy range (below TeV and above EeV) are
under way.


\section{References}

%\vspace{\baselineskip}

\re
1.\ Andres E.\ et al.\ 2000, Astropart. Phys. 13, 1
\re
2.\ http://icecube.wisc.edu/
\re
3.\ Gaisser T. for the IceCube collaboraiton, this conference.
\re
4.\ Ahrens J.\ et al.\ 2003 astro-ph/0305196, submitted to Astropart.Phys.
\re
5.\ Mannheim K., Protheroe R. J., Rachen J. P.\ 2001, Phys. Rev. D 63, 023003
\re
7.\ Stecker F. W., Salomon M. H.\ 1996, Space Sci. Rev. 75, 341.
\re
8.\ Waxman E., Bahcall J.\ 1999, Phys. Rev. D 59, 023002


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