Thursday, November 21, 2013

IceCube World's largest particle detector detects first high-energy neutrinos from the cosmos

This is the highest energy neutrino ever observed, with an estimated energy of 1.14 PeV. 

It was detected by the IceCube Neutrino Observatory at the South Pole on Jan. 3, 2012. IceCube physicists named it Ernie.

Twenty-eight events with energies around and above 30 TeV were observed in an all-sky search, conducted between May 2010 and May 2012, for high-energy neutrino events with vertices contained in the IceCube neutrino detector. Credit: Credit: IceCube Collaboration

The IceCube Neutrino Observatory, a particle detector buried in the Antarctic ice, is a demonstration of the power of the human passion for discovery, where scientific ingenuity meets technological innovation.

Today, nearly 25 years after the pioneering idea of detecting neutrinos in ice, the IceCube Collaboration announces the observation of 28 very high-energy particle events that constitute the first solid evidence for astrophysical neutrinos from cosmic accelerators.

Francis Halzen
"This is the first indication of very high-energy neutrinos coming from outside our solar system, with energies more than one million times those observed in 1987 in connection with a supernova seen in the Large Magellanic Cloud," says Francis Halzen, principal investigator of IceCube and the Hilldale and Gregory Breit Distinguished Professor of Physics at the University of Wisconsin–Madison.

"It is gratifying to finally see what we have been looking for. This is the dawn of a new age of astronomy."

Details of the research appear in a manuscript published in the Nov. 22, 2013 issue of the journal Science.

Because they rarely interact with matter, the nearly massless subatomic particles called neutrinos can carry information about the workings of the highest-energy and most distant phenomena in the universe.

Gregory Breit
Billions of neutrinos pass through every square centimeter of the Earth every second, but the vast majority originate either in the sun or in the Earth's atmosphere.

Far rarer are neutrinos from the outer reaches of our galaxy or beyond, which have long been theorized to provide insights into the powerful cosmic objects where high-energy cosmic rays may originate: supernovas, black holes, pulsars, active galactic nuclei and other extreme extragalactic phenomena.

IceCube, run by the international IceCube Collaboration and headquartered at the Wisconsin IceCube Particle Astrophysics Center (WIPAC) at UW–Madison, was designed to accomplish two major scientific goals: measure the flux, or rate, of high-energy neutrinos, and try to identify some of their sources.

This is an artistic rendering of IceCube DOMs below the Antarctic ice. Inside IceCube, a total of 5,160 sensitive detectors hang from 86 steel cables. 

Credit: Jamie Yang, The IceCube Collaboration.

The analysis presented in the Science paper reveals the first high-energy neutrino flux ever observed, a highly statistically significant signal (more than 4 sigma) that meets expectations for neutrinos originating in cosmic accelerators.

"From hints in earlier IceCube analyses, we have used improved analysis methods and more data to make a significant step forward in our search for the elusive astrophysical signal," says collaboration spokesperson Olga Botner, of Uppsala University.

"We are now working hard on improving the significance of our observation, and on understanding what this signal means and where it comes from."

More information: Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector; The IceCube Collaboration; Science (2013); DOI: 10.1126/science.1242856

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