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The Hunt for Neutrinos

Phantom Detectors
an overhead view of AMANDA
  Photo: John Jacobsen
  Hoses carrying hot water melt their way into the ice. The hot water is used to drill the deep columns into which the optical sensors are placed.
 

Neutrino detection is tricky business. The instrument must be big enough to detect the rare neutrino interaction, transparent enough to track a muon's path across a great distance, and far enough below the Earth's surface to filter out interference from irrelevant particles and light. As it turns out, the extraordinary clarity of the deep Antarctic ice provides an ideal medium.

Buried nearly a mile and a half beneath the Polar ice cap, AMANDA acts more like a telescope than a traditional particle detector, collecting rather than creating particle debris. But while most telescopes search the skies with optical lenses and mirrors to capture celestial light, this one uses phototubes in glass orbs to scrutinize the subterranean ice for the light that heralds a neutrino's passing. Nearly seven hundred of these glass detectors are placed throughout the ice, strung on nineteen cables lowered deep into narrow columns of melted ice, where they freeze in place. You can see how these parts of the detector are set up in a variety of schematic diagrams of the detector.

As neutrinos bombard the sunken detectors, a few interact with subatomic particles in the ice and rock and create muons. Essentially a heavy electron, the negatively charged muon emits a faint blue light that illuminates the phototubes.

Acting like light bulbs in reverse, the phototubes collect a muon's light and convert it into electrical signals, which are sent to computers above the ice that store and process the data. The signals announce the presence of a neutrino arrival, as well as its rate, frequency, and path. Researchers hope to trace the muon's path back to the neutrino's cosmic origins.

To mine the full potential of the deep, clear Antarctic ice, scientists plan to outfit AMANDA with as many as 50,000 orbs on 80 cables over the next decade. As they push the limits of engineering and endurance, researchers sense the discovery of something truly monumental—though they're not sure what. They'll just have to wait till the heavens send them the clues.

To learn more about AMANDA:

AMANDA Web page:
http://amanda.berkeley.edu/amanda/amanda.html

The Center for Astrophysical Research in Antarctica:
http://astro.uchicago.edu/cara/

 

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