IceCube, a telescope under construction at theSouth Pole, will peer through the earth to open a
new window onto the universe. Like its
predecessor, AMANDA (see below), IceCube will
search for neutrinos from the most violent
astrophysical sources: events like exploding stars,
gamma ray bursts, and cataclysmic phenomena
involving black holes and neutron stars. The
IceCube telescope is a powerful tool to search fordark matter, and could reveal the new physicalprocesses associated with the enigmatic origin of
the highest energy particles in nature.
Rather than using light, this “new window” on theuniverse opens using a novel astronomical
messenger called a neutrino. IceCube will probe
the universe by detecting these elusive subatomic
particles hurtling through space. Since the 1950sscientists have built a compelling scientific case fordoing astronomy and particle physics using highenergy neutrinos. The challenge has been one oftechnology to build the kilometer-sized observatoryneeded to do the science.
During the last decade, an international
collaboration of scientists constructed andoperated the first high-energy neutrino telescope.
Completed in the year 2000, the Antarctic Muon
and Neutrino Detector Array (AMANDA) has
transformed part of the Antarctic icecap into aparticle detector. AMANDA scientists positioned
about 750 optical sensors deep in this ice.
The faint flashes of light created by neutrinos
moving through the transparent ice are detectedby these optical sensors. Its setting in the remotepolar ice is one of many reasons Scientific
American distinguished AMANDA as the “weirdest”
of its “seven wonders of modern astronomy”(1999).
IceCube will encompass a cubic kilometer of ice.
Theorists anticipate that an instrument of thissize is required to study neutrinos from distantastrophysical sources. AMANDA demonstrated theviability of a neutrino telescope in ice by detecting

high-energy neutrinos produced in the earth’s
atmosphere near the North Pole! With AMANDA
as its proof-of-concept, an international
collaboration is constructing IceCube to peer deep
into the cosmos.
Why use neutrinos to peer into the universe?
Neutrinos are produced by the decay ofradioactive elements and elementary particles
such as pions. Unlike other particles, neutrinos areantisocial, difficult to trap in a detector. The
existence of neutrinos was first suspected in 1930
when scientists observed that energy andmomentum were missing from the decay ofradioactive nuclei. It was not until 1955 thatneutrinos were finally observed, a discovery forwhich Frederick Reines received the Nobel Prize.
In 2001, experiments observing the sun revealed
that neutrinos have tiny but definitely non-zeromasses. This mysterious particle remains a hot
topic in particle physics, astrophysics andcosmology.
It is the feeble interaction of neutrinos with matterthat makes them uniquely valuable asastronomical
messengers.
Unlikephotons orcharged
particles,
neutrinos
can emerge
from deep
inside theirsources andtravel acrossthe universe
without
interference.
They are notdeflected byinterstellar
magnetic•
The IceCube
telescope andits predecessor,
AMANDA, use
optical sensors
to locate thesources of highenergy
neutrinos. This
picture shows
the on-line
display of aneutrino event
recorded by
AMANDA.

Neutrinos
emitted bydistant cosmic
sources cantravel directly
throughintervening
matter in space
and the earth tothe IceCube
telescopeembedded
below thesurface of theSouth Pole.

••
IceCube willencompass
AMANDA(yellowcylinder). Itsmuch larger
size improves
both theaccuracy withwhich we canproject theorigin of adetectedneutrino, andour capacity tomeasure its
energy. Here,the color codingof the sensors,
following therainbow from
red to purple,
labels passageof time along
the particle
track

fields and are not absorbed by intervening matter.
However, this same trait makes cosmic neutrinos
extremely difficult to detect; immense instruments
are required to find them in sufficient numbers totrace their origin.
Muons—how to see the invisible neutrino
Although trillions of neutrinos stream through yourbody every second, none may leave a trace inyour lifetime. We actually use large volumes of ice
below the South Pole to watch for the rare
neutrino that crashes into an atom of ice. This
collision produces a particle—dubbed a “muon”—
that emerges from the wreckage. In the ultratransparent ice, the muon radiates blue light that is
detected by IceCube’s optical sensors. The muonpreserves the direction of the original neutrino,
thus pointing back to its cosmic source. It is bydetecting this light that scientists can reconstruct
the muon’s, and hence the neutrino’s, path.

•Emerging froma crash with aneutrino, amuon preserves
the neutrino’s
trajectory andemits blue lightthat thetelescope’ssensors detect.

Map ofAntarctica, from
USARC Atlas ofAntarcticResearch.
Covered by a
deep ice cap,
the South Poleis the perfectlocation forIceCube.

•• transparent enough to allow light to travel
through a widely spaced array of optical sensors;• dark enough to avoid the interference of naturallight;• deep enough below the earth’s surface to avoid
interference from southern hemisphere cosmicrays; and• cheap enough to build.
Only dark oceans or deep fields of ice meet allthese constraints. Indeed, Antarctic polar ice hasturned out to be an ideal medium for detecting
neutrinos. It is exceptionally pure, transparent andfree of radioactivity. A mile below the surface, blue
light travels a hundred
meters or more throughthe otherwise dark ice.

The picture is radically complicated by the fact thatmost muons seen by IceCube have nothing to dowith cosmic neutrinos. Unfortunately, for every
muon from a cosmic neutrino, IceCube detects
about a million more muons produced by cosmic
rays in the atmosphere above the detector. To filter
them out, telescopes such as AMANDA andIceCube take advantage of the fact that neutrinos
interact so weakly with matter. Because neutrinos
are the only known particles that can pass throughthe earth unhindered, AMANDA and IceCube lookthrough the earth and to the northern skies, using
the planet as a filter to select neutrinos.
Why Antarctic Ice?
A neutrino telescope must be:• large enough that some of the rare galactic andextra-galactic neutrinos interact as they pass by;True, it is difficult tofind a more remotelocation for atelescope. But
experience with
AMANDA has clearly
demonstrated that theSouth Pole’s advantages
outweigh its relative inaccessibility. AMANDA andIceCube:• deploy sensors from the solid, stable surface of
the ice rather than from a ship;• collect the data in electronic instruments housed
directly above the telescope rather than miles
away at a shore station; and• exploit the infrastructure of the recently
renovated U.S. Amundsen-Scott South PoleStation.

Frozen in the ice, IceCube not only will be thelargest and most durable particle detector, but areal bargain at just 25 cents per ton!
How does IceCube “see” a neutrino?
Like its predecessor, AMANDA, the basic
component of IceCube is the sensor thattransforms light into electrical signals. A sensor isa photomultiplier tube housed in aglass pressure vessel; IceCube
will boast nearly 5000. The
technology used in IceCube
will be more advanced thanthat of AMANDA. IceCube
will have “smart”

sensors,
meaning thateach sensor willcontain a computer chip connected through theinternet to computers in scientists’ offices! It is not
too fanciful to think of the device as a cubickilometer, continuously sensing computer.
We attach 60 optical modules on a long electricalcable—likebeads on astring—that isconnected to asignalprocessing
facility on thesurface. To
position thisstring ofmodules, drillers usea 5 megawatt jet of
hot water to melt ahole a bit wider thanhalf a meter and 2.4
kilometers deep. We
then have roughly a
day to lower the stringof sensors before thewater refreezes.
IceCube will takeadvantage ofimproved drilling
technology developed
during theconstruction of
AMANDA to meet an ambitious deployment
schedule of 80 strings with 60 optical sensors eachin just 6 years. Improved digital sensor technology,
combined with the overall size of the telescope,will greatly increase the scientific potential of
IceCube over its trail-blazing predecessor,
AMANDA.

•The summer
drilling camp at
Amundsen-Scott
South PoleStation.

•Eva Dahlberg
preparing a
module to belowered into a
temporary holein the ice.

Each opticalmodule consistsof aphotomultipliertube housed ina glasspressurevessel.

•
Endless frontiers
Having no electrical charge and interacting weakly
with matter, neutrinos are special astronomical
messengers. Only they can carry information
directly from violent cosmological events at theedge of the universe or from the hearts of black
holes.
The history of astronomy shows that work in newenergy regions has invariably resulted in the
discovery of totally unexpected phenomena. By
peering through a new window on the universe,
IceCube promises findings that will open newfrontiers of understanding.

IceCube will
occupy a
volume of one
cubic kilometer.
Here we depict
one of the 80
strings of opticalmodules(number andsize not toscale). IceTop,located at thesurface,comprises anarray of sensors
to detect airshowers. It will
be used tocalibrate
IceCube and toconduct
research on
high-energy
cosmic rays.

•Optical modules
are strung onelectrical cables
like beads on astring andfrozen morethan 1500
meters below
the surface ofthe ice.

•A physics
graduatestudent, Jodi
Cooley (right),
describes tohigh school•
physics
students theworkings of aphotomultipliertube, the opticalsensor housedin each glass
module.

Participating Institutions•Education and outreach
AMANDA and IceCube scientists and engineers are not only building andanalyzing data from these remote and unique
instruments. They also are enabling others toexperience the excitement of learning anddiscovery that they feel. They believe that,parallel with the transformations in science that
accompany the development of major new
instruments, there should be improvements inthe ways all students and the public learn
about and participate in science. The IceCube
Education Resource Center is helping thesescientists develop excellent educational
resources, and generate meaningful ways tocommunicate with people—young and old, in all walks of life, and with different
levels of interest in this new frontier of particle astrophysics.
Chiba University, Japan

Université de Mons-Hainaut, Belgium

Clark Atlanta University, USA

University of Alabama, USA

DESY - Zeuthen, Germany

University of California–Berkeley, USA

Institute for Advanced Study, USA

University of Delaware, USA

Lawrence Berkeley National Laboratory, USA

University of Kansas, USA

South Pole Station, Antarctica

University of Maryland, USA

Southern University and A & M College, USA

University of Pennsylvania, USA

Stockholm Universitet, Sweden

University of Wisconsin–Madison, USA (lead)

Universität Mainz, Germany

University of Wisconsin–River Falls, USA

Universität Wuppertal, Germany

Uppsala Universitet, Sweden

Université Libre de Bruxelles, Belgium

Vrije Universiteit Brussel, Belgium

Agencies supporting AMANDA/IceCube include:• German Ministry of Research and Education• German Research Foundation (DFG)• Knut and Alice Wallenberg Foundation, Sweden• National Fund for Scientific Research, Belgium• Swedish Natural Science Research Council• Swedish Polar Research Secretariat• University of Wisconsin Alumni Foundation• U.S. National Energy Research Scientific Computing Center(supported by the Office of Energy Research of the U.S. Department ofEnergy)• U.S. National Science Foundation, Office of Polar Programs• U.S. National Science Foundation, Physics Division

http://icecube.wisc.edu/Version 1, June 2002