Berkeley Lab Researchers Part of an International Hunt
November 21, 2013
Lynn Yarris (510) 486-5375 lcyarris@lbl.gov
In our universe there are particle accelerators 40 million times more powerful than the Large Hadron Collider (LHC) at CERN. Scientists don’t know what these cosmic accelerators are or where they are located, but new results being reported from “IceCube,” the neutrino observatory buried at the South Pole, may show the way. These new results should also erase any doubts as to IceCube’s ability to deliver on its promise.
IceCube is a neutrino observatory whose detectors are buried more than a mile below the surface of the South Pole. (Photo by Emanuel Jacobi of the National Science Foundation)
“The IceCube Collaboration has announced the observation of 28 extremely high energy events that constitute the first solid evidence for astrophysical neutrinos from outside our solar system,” says Spencer Klein, a senior scientist with Lawrence Berkeley National Laboratory (Berkeley Lab) and a long-time member of the IceCube Collaboration. “These 28 events include two of the highest energy neutrinos ever reported, which have been named Bert and Ernie.”
Lisa Gerhardt and Spencer Klein with an IceCube Digital Optical Module (DOM). IceCube employs 5,160 DOMs to detect the Cherenkov radiation emitted by high-energy neutrino events in the ice. (Photo by Roy Kaltschmidt)
The new results from IceCube, which were published in the journal Science, provide experimental confirmation that somewhere in the universe, something is accelerating particles to energies above 50 trillion electron volts (TeV) and, in the cases of Bert and Ernie, exceeding one quadrillion electron volts (PeV). By comparison, the LHC accelerates protons to approximately four TeV in each of its beams. While not telling scientists what cosmic accelerators are or where they’re located, the IceCube results do provide scientists with a compass that can help guide them to the answers.
The IceCube observatory consists of 5,160 basketball-sized light detectors called Digital Optical Modules (DOMs), which were conceived and largely designed at Berkeley Lab. The DOMS are suspended along 86 strings that are embedded in a cubic kilometer of clear ice starting one and a half kilometers beneath the Antarctic surface. Out of the trillions of neutrinos that pass through the ice each day, a couple of hundred will collide with oxygen nuclei, yielding the blue light of Cherenkov radiation that IceCube’s DOMs detect.
Cherenkov radiation glowing in the core of the Advanced Test Reactor
“Each of IceCube’s DOMs was designed to be a mini-computer server that you can log onto and download data from, or upload software to,” says Robert Stokstad, a senior scientist with Berkeley Lab’s Nuclear Science Division who led the development of the DOMs and was one of the original proponents of IceCube. “It is rewarding to see how well they are performing.”
The 28 high-energy neutrinos reported in Science by the IceCube Collaboration were found in data collected from May 2010 to May 2012. In analyzing more recent data, Berkeley Lab’s Lisa Gerhardt discovered another event that was almost double the energy of Bert and Ernie. Dubbed “Big Bird,” this new event was presented by Klein at the International Cosmic-Ray Conference.
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