Polar neutrino observatory takes a big step forward (Forwarded)

University Communications
University of Wisconsin-Madison

March 21, 2006

Polar neutrino observatory takes a big step forward
By Terry Devitt

An international team of scientists and engineers has taken a major step
toward completion of what will be the world's preeminent cosmic neutrino
observatory, harnessing a sophisticated hot-water drill to build an
observatory under the South Pole that eventually will encompass a cubic
kilometer of ice.

Scientists leading a consortium building the massive neutrino telescope
known as IceCube say that this year they have nearly doubled the size of
the detector now under construction at the National Science Foundation's
Amundsen-Scott South Pole Station.

NSF, through a joint program of its Office of Polar Programs and its
Mathematical and Physical Sciences Directorate, is contributing more
than $240 million to the international partnership that is building the
detector, which will cost $272 million overall.

Although work can only take place from October through February -- the
fleeting and still frigid summer season at the Pole -- the extent and
pace of construction this year means that the observatory may soon begin
scientific operations. IceCube is scheduled for completion in 2011.

"The news is good all around," says Francis Halzen, the UW-Madison
physics professor leading the effort.

Halzen and others leading the effort report that IceCube -- which
depends on strings of light-sensing modules frozen deep in crystal clear
Antarctic ice -- has grown this austral summer by 480 basketball-sized
optical modules. Deployed on long cables in 1.5-mile deep holes bored by
a unique hot-water drill, the modules will be used to detect the
fleeting but telltale signatures of high-energy cosmic neutrinos as they
flit through the Earth.

Neutrinos are ghostly, high-energy subatomic particles created in
galactic collisions, distant black holes, quasars and a zoo of the most
violent events in the cosmos. They carry information that promises to
peel back some of the mystery of the universe's most enigmatic events
such as gamma ray bursts, dark matter and supernovas.

But cosmic neutrinos -- billions of which pass unnoticed through the
Earth and indeed through the human body every day -- are, by their very
nature, extremely difficult for astrophysicists to detect. What is
required is a very large detector to optimize the chances that
scientists can catch a neutrino in the act of crashing into a proton or
another subatomic particle.

When IceCube is completed, a cubic kilometer of the ice beneath the Pole
will have been seeded with more than 4,200 optical sensors to capture
telltale traces of the neutrinos and follow their tracks back to their
distant points of origin. In addition, another 300 or so sensors will be
deployed in tanks on the surface of the polar ice.

Once the holes are drilled, cables with the spherical digital optical
modules -- which are composed of electronics for sensing light and
circuit boards for gathering and processing data -- are lowered into the
ice, where they are frozen in place. The modules act like light bulbs in
reverse, gathering light created when neutrinos collide with other
particles. The modules then relay data to the surface where the
information is processed and stored for analysis.

When fully operational, IceCube will sample neutrinos from the sky in
the Northern Hemisphere. The detector will use the Earth as a filter to
exclude other types of neutrinos, such as those from the sun, which
could confuse the detector. Its primary scientific mission will be to
identify the sources and distribution of the highest energy neutrinos
created by violent cosmic events.

IceCube is being constructed around an older, prototype neutrino
telescope known as AMANDA for Antarctic Muon and Neutrino Detector
Array. IceCube construction began in January 2005 when scientists
drilled the first hole for the detector and deployed the first optical
modules for the observatory.

"The digital optical modules deployed last year have now functioned for
one year without failures," says Halzen. "They perform like a Swiss
watch. But the big story of this season is the performance of the drill."

After working out kinks in the performance of the drill last year and at
the beginning of the 2005-06 drilling season, and adding an extra
drilling tower, the IceCube team was able this year to bore a total of
eight deep holes into the Antarctic ice and deploy eight 60-module
strings of sensors this season. Combined with the existing AMANDA array,
IceCube currently consists of nearly 1,300 optical modules.

Although the new technologies used to create the detector are completely
environmentally safe, the engineering challenges of working in the Polar
environment -- where temperatures fluctuate, on average, from minus 35
Fahrenheit in November to minus 16 Fahrenheit in February -- are
daunting. Even so, "all the major challenges encountered by drilling a
first hole last season have been solved," says Halzen.

The IceCube array now is composed of nine strings and 16 surface
detector stations, in addition to the still operational AMANDA array,
making a scientific program possible, according to Jim Yeck, IceCube
project director.

"We know that there is more work to be done, but let there be no doubt
about what a remarkable accomplishment it is to safely install eight
strings this season," Yeck says.

The newly installed modules are functioning and sending signals to the
surface, Yeck says. IceCube scientists will continue to verify cable
connections and surface electronics during the upcoming winter season at
the South Pole.

IceCube is an international collaboration of scientists from more than
30 scientific organizations. It is supported primarily by NSF, with
significant contributions from Germany, Sweden, Belgium, Japan, New
Zealand, and the Netherlands. The project has also received significant
support from the Wisconsin Alumni Research Foundation.

Scientists collaborating on IceCube include researchers from UW-Madison,
the University of California at Berkeley, the University of California
at Irvine, the Lawrence Berkeley National Laboratory, the University of
Maryland, Penn State University, the University of Wisconsin-River
Falls, the University of Delaware, the University of Kansas, Clark
Atlanta University, Southern University, the University of Alaska, and
the Institute for Advanced Study at Princeton University.

IMAGE CAPTIONS:

[Image 1:
http://www.news.wisc.edu/newsphotos/...ce_shaft06.jpg (1.6MB)]
Cables snake down one of the eight 1.5 mile-deep holes drilled this year
in the Antarctic ice for project IceCube, a massive neutrino telescope
being constructed at the South Pole. The international project, led by
UW-Madison physics Professor Francis Halzen, made significant progress
this austral summer, adding 480 basketball-sized optical modules used to
track signs of cosmic neutrinos. When completed, the neutrino
observatory will occupy a cubic kilometer of Antarctic ice, and will be
the world's largest scientific instrument.

Photo: courtesy Ice Cube Project

[Image 2:
http://www.news.wisc.edu/newsphotos/...e_sensor06.jpg (1.7MB)]
Robert Paulos, associate director for the IceCube project, holds one of
the digital optical modules that power the IceCube neutrino telescope.

Photo: courtesy Ice Cube Project