An team of international experts has announced a new observation of high-energy neutrino particles using an instrument funded by the National Science Foundation (NSF). The particles from beyond our galaxy have been detected at the geographic South Pole, using a massive instrument buried deep in ice.
The scientists from the IceCube Collaboration, a research team with headquarters at the Wisconsin IceCube Particle Astrophysics Center at the University of Wisconsin-Madison, published their new discovery in the journal Physical Review Letters, on August 20, 2015. The new observation confirmed an initial detection of high-energy neutrinos made in November 2013.
Billions of subatomic neutrino particles pass through our planet on a daily basis, however, they cannot be directly observed. For that reason, IceCube Neutrino Observatory, a one cubic kilometer sized detector was sunk into the ice sheet at the South Pole which allowed the scientists to indirectly observe the particles, by detecting the products of their interaction with ice sheets.
Neutrino particles travel throughout the universe, almost entirely undisturbed by matter and pointing to the sources of their creation. The highest energy neutrinos presumably originate from the most extreme phenomena of the universe, which are able to generate energies million times more powerful than those generated by a man-made source such as the Large Hadron Collider at CERN.
"Cosmic neutrinos are the key to yet unexplored parts of our universe and might be able to finally reveal the origins of the highest energy cosmic rays, including the rare 'Oh-My-God' particles," says IceCube Collaboration spokesperson Olga Botner, of Uppsala University.
The observatory records 100 000 neutrino particle every year. Most of them are called muons and they are generated during the cosmic ray interaction with the Earth's atmosphere. To detect other types of neutrino particles, the researchers have used planet Earth to filter out the large background of atmospheric muons. By observing neutrinos from the Northern Hemisphere, they have confirmed the cosmic origin of the particles, as well as the presence of extragalactic neutrinos and the intensity of the neutrino rate.
"Looking for muon neutrinos reaching the detector through the Earth is the way IceCube was supposed to do neutrino astronomy and it has delivered," said Francis Halzen, IceCube principal investigator and the Hilldale and Gregory Breit Distinguished Professor of Physics at the University of Wisconsin-Madison. "This is as close to independent confirmation as one can get with a unique instrument."
New results agree with the previous and confirm the higher number of neutrinos originating beyond our Solar System. The new high-energy neutrino sample allows the most accurate measurements to date of the energy spectrum and neutrino-type composition of the extraterrestrial neutrino flux, when combined with previous measurements.
"This is an excellent confirmation of IceCube's recent discoveries, opening the doors to a new era in particle physics," says Vladimir Papitashvili, astrophysics and geospace sciences program director in the Division of Polar Programs. "And it became possible only because of extraordinary qualities of Antarctic ice and NSF's ability to successfully tackle enormous scientific and logistical problems in the most inhospitable places on Earth."
- "Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube" - M. G. Aartsen et al. (IceCube Collaboration) - Physical Review Letters (2015) - doi: http://dx.doi.org/10.1103/PhysRevLett.115.081102