A massive telescope buried in the Antarctic ice has detected 28 extremely high-energy neutrinos—elementary particles that likely originate outside our solar system. Two of these neutrinos had energies many thousands of times higher than the highest-energy neutrino that any man-made particle accelerator has ever produced, according to a team of IceCube Neutrino Observatory researchers that includes Penn State scientists. These new record-breaking neutrinos had energies greater than 1,000,000,000,000,000 volts or, as the scientists say, 1 peta-electron volt (PeV).
"Scientists have been searching high and low for these super-energetic neutrinos using detectors buried under mountains, submerged in deep lakes and ocean trenches, lofted into the stratosphere by special balloons, and in the deep clear Antarctic ice at the South Pole," said Penn State Professor of Physics and Astronomy and Astrophysics Doug Cowen, who has worked on IceCube for over a decade. "To have finally seen them after all these years is immensely gratifying." The discovery was announced this week at the IceCube Particle Astrophysics Symposium in Madison, Wisconsin.
Because high-energy neutrinos rarely interact with matter and are not deflected by magnetic fields in our galaxy, they can carry information about the workings of the highest-energy and most-distant phenomena in the universe. But although billions of neutrinos pass through the Earth every second, the vast majority are lower-energy particles that originate either in the Sun or in the Earth's atmosphere. Far rarer are the high-energy neutrinos that more likely would have been created much farther from Earth in the most powerful cosmic events -- gamma ray bursts, black holes, or the birth of stars.
"While it is premature to speculate about the precise origin of these neutrinos, their energies are too high to be produced by cosmic rays interacting in the Earth's atmosphere, strongly suggesting that they are produced by distant accelerators of subatomic particles elsewhere in our galaxy, or even farther away," said Penn State Associate Professor of Physics Tyce DeYoung, the deputy spokesperson of the IceCube Collaboration.
IceCube is the world's largest observatory ever built to detect the elusive sub-atomic particles called neutrinos.
The IceCube collaboration is continuing to refine and expand the search with new data and new analysis techniques, which may reveal additional high-energy events and possibly point to their astrophysical source or sources. "Although further observations will be required to confirm the extraterrestrial origin of these neutrinos, after more than ten years of work building this detector, it's very exciting to see what may be the first glimpse of a new window on our universe," DeYoung said.
The IceCube Collaboration, which includes several Penn State faculty, postdoctoral, graduate and undergraduate researchers, reported 28 high-energy neutrino events captured by the detector between May 2010 and May 2012. These events, including two that exceeded the unprecedented energy level of 1 PeV, were among the main goals for building the IceCube detector.
IceCube is comprised of more than 5,000 digital/optical modules melted into in a cubic kilometer of ice at the South Pole. The observatory, supported by the U.S. National Science Foundation, detects neutrinos through the fleeting flashes of blue light produced when a neutrino interacts with a water molecule in the ice.
The first hints of high-energy neutrinos came with the discovery in April 2012 of two neutrinos with energies in excess of 1 PeV. An analysis of those events was reported recently in a paper submitted to the journal Physical Review Letters. An intensified follow-up search turned up 26 additional events exceeding 30 tera-electron volts (the energy of one TeV is one-thousandth that of a PeV). The results of this follow-up search will be described in a forthcoming paper in a scientific journal.
The IceCube Neutrino Observatory was built under a National Science Foundation (NSF) Major Research Equipment and Facilities Construction grant, with assistance from partner funding agencies in Germany, Sweden, and Belgium. The NSF Division of Polar Programs continues to support the project with a Maintenance and Operations grant, in conjunction with support from international scientific funding agencies. The scientific collaboration includes 250 physicists and engineers from the U.S., Germany, Sweden, Belgium, Canada, Switzerland, Japan, New Zealand, and Australia.
Source: Penn State University