Researchers Publish on Recent Neutrino Observation

Department of Physics and Astronomy researchers were part of the exciting recent announcement of the scientific observation of 28 very high-energy particle events. These events were the first solid evidence for astrophysical neutrinos which were captured with cosmic accelerators at the IceCube Neutrino Observatory, a particle detector buried in the Antarctic ice.

Details of the research appeared in Science last month. Co-authors on the paper included Dr. Patrick Toale, assistant professor in the Department of Physics and Astronomy, Dr. Pavel Zarzhitsky, a former UA post-doctoral researcher, and UA graduate students Michael Larson, James Pepper and Donglian Xu.

“We believe we are seeing, for the first time, extremely high-energy neutrinos from a source outside of our solar system,” said Dr. Dawn Williams, an associate professor in the Department of Physics and Astronomy, who serves as the project’s calibration coordinator.

Neutrinos, which are nearly massless subatomic particles, can carry information about the workings of the highest-energy and most distant phenomena in the universe because they rarely interact with matter. Billions of neutrinos pass through every square centimeter of the Earth every second, but the vast majority of them 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 powerful cosmic objects like 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 at the University of Wisconsin–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.

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

The 28 high-energy neutrinos were found in data collected by the IceCube detector from May 2010 to May 2012. The events cannot be explained by other neutrino fluxes, such as those from atmospheric neutrinos, or by other high-energy events, such as elementary particles known as muons that are produced by the interaction of cosmic rays in the atmosphere.

UA’s portion of the funding connected with this research comes from an approximate $500,000 National Science Foundation grant awarded to Williams that continues through 2015.