Doing astronomy with neutrinos

The IceCube detector, located at the South Pole, monitors a cubic kilometer of ice for the flashes of light produced as energetic particles traverse the ice. Each second, about 3,000 muons, produced by cosmic rays slamming into the atmosphere, interact with matter in the detector. In contrast, neutrinos are only detected once every six minutes.

Francis Halzen, the principle investigator for IceCube, described the search for these particles in the detector at the recent meeting of the American Association for the Advancement of Science. "It's like doing astronomy, but the sky is cloudy," he said. "It's cloudy all the time." Even the majority of the neutrinos that arrive at the detector aren't especially interesting; they're also produced as part of cosmic ray particle showers. Instead, the computers behind the detectors have to sort through 100 billion muons each year, along with 100,000 atmospheric neutrinos, just to find about 10 interesting events.

But the interesting events are incredibly energetic. "When it arrives, it hits your detector like a hammer," Halzen told the audience. "You don't have to look for it; it just announces itself." (The same goes for some of the energetic muons, two of which have deposited over 560 Tera electron Volts in the detector—compare that to the LHC's upcoming 14TeV collisions.)

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