Volume 13, Number 3, 2005
Working under harsh conditions, an international team that includes scientists from the Department of Physics and Astronomy’s Bartol Research Institute has set in place the first critical elements of a massive neutrino telescope at the South Pole.
Sixty optical detectors designed to sample phantom-like, high-energy particles from deep space have been installed in a hole drilled 1.5 miles into the Antarctic ice. Researchers say the successful deployment of these detectors represents a key first step in the construction of the $272 million telescope known as IceCube.
The overall project is led by the University of Wisconsin at Madison and also includes an array of detectors on the surface, known as IceTop, for which UD is the lead institution.
The National Science Foundation will provide $242 million to finance the telescope and its construction, with an additional $30 million from international partners.
“We successfully installed four surface stations,” Thomas K. Gaisser, Martin A. Pomerantz Chair of Physics and Astronomy, says. Each station consists of two tanks of ice viewed by the same optical modules used in the deep detector.
The team works in Antarctica during the Southern Hemisphere summer. When the most recent work concluded in February, members declared a successful first season of construction on what will become the world’s largest scientific instrument. Scientists and project managers will return to Antarctica in November.
“It’s all on track,” Francis Halzen, a University of Wisconsin-Madison professor of physics and the principal investigator for the project, said in the February announcement. “This was our first exam. We met our milestones for the season, and we can move on to the next Antarctic summer.”
Halzen said building the telescope requires drilling at least 70 holes in the Antarctic ice, each 1.5 miles deep, using a novel hot-water drill. Workers then lower long strings of volleyball-sized optical detectors--4,200 in all--into the holes, where they are frozen in place. The 140 IceTop tanks will contain an additional 280 detectors.
The first string, with 60 detectors, was successfully lowered into the ice in late January, and communication with the detectors, each of which is like a small computer, has been successfully established.
When completed, the telescope will use a cubic kilometer of Antarctic ice as a detector and will be capable of capturing information-laden, high-energy particles from some of the most distant and violent events in the universe. It promises a new window to the heavens and may be astronomy’s best bet to resolve the century-old quest to identify the sources of cosmic rays.
The IceCube telescope will look for the telltale signatures of high-energy cosmic neutrinos, ghostlike particles produced in such violent cosmic events as colliding galaxies, distant black holes, quasars and other phenomena occurring at the very margins of the universe. Cosmic rays, which are composed of protons, are thought to be generated by these same events. But, protons are bent by the magnetic fields of interstellar space, preventing scientists from following them back to their points of origin.
Cosmic neutrinos, on the other hand, have the unique ability to travel cosmological distances without being absorbed or deflected by the stars, galaxies and interstellar magnetic fields that permeate space. Their ability to skip through matter without missing a beat promises unedited information about the early universe and the very violent objects that populate deep space.
However, that same phantom-like ability to travel billions of light years and pass unhindered through planets, stars and galaxies makes detecting cosmic neutrinos extraordinarily difficult.
“Neutrinos travel like bullets through a rainstorm,” Halzen says. “Immense instruments are required to find neutrinos in sufficient numbers to trace their origin.”
The IceTop surface array “will detect and study events produced by high-energy cosmic-ray particles interacting in the atmosphere above IceCube,” Gaisser said. “Such downward events produce the main background in the deep neutrino telescope, so tagging them with the surface array will improve the signal-to-background ratio of the instrument. Events detected in coincidence by both the surface and the deep detectors also carry information about the origin of the cosmic rays of very high energy. This information will be complementary to that obtained from the upward events in the neutrino telescope.”
“If we stay on schedule, IceCube could take over next year as the world’s largest neutrino telescope,” Halzen says.
Several representatives of UD were at the South Pole working on the project during the first construction season. Joining Gaisser were physics Prof. Paul Evenson, senior electronics specialist James Roth and scientist Serap Tilav, AS ’86M, ’91PhD. Also working on the IceTop project from the University are David Seckel, professor of physics; Todor Stanev, professor of physics; senior scientist John Clem; scientists Stoyan Stoyanov and Xinhua Bai; researchers Peter Niessen and Tonio Hauschildt; and graduate students Divya Swarnkar and Nehar Arora.
—Neil Thomas, AS ’76