IceCube Observatory in Antarctica Confirms Detection of Most Energetic Neutrinos Ever

The IceCube neutrino observatory, a particle detector encompassing a cubic kilometer of ice at the South Pole that records the interactions of the nearly massless sub-atomic particle, recorded a very rare event never seen before. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. These neutrinos have extremely high energies, hundreds of times larger than the energy of a proton at the LHC super collider.

In a paper submitted to Physical Review Letters, the IceCube Collaboration confirms that the two events of neutrinos with over one peta electron volt (PeV) that were announced last year are most likely no false signals and are thus the two highest energy neutrinos ever observed. The events have estimated energies of 1.04 ± 0.16 and 1.14 ± 0.17 PeV, validating the ability of IceCube to detect such neutrinos.

The IceCube telescope, the world's largest neutrino detector, is also a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams.

Most of the neutrinos reaching the Earth originate either in the Sun or in our atmosphere through the interaction of incoming cosmic rays. However, if we look at neutrino energy, once we reach the PeV scale (the energy equivalent to 1,000,000 times the mass of a proton), neutrinos coming from far off in our galaxy or from more distant places in the visible Universe become dominant.

IceCube researchers have estimated that the probability that these two events are not background, i.e., anything else in the detector besides astrophysical neutrinos, is at the 2.8 sigma level -- with 2.8 standard deviations equal to about 99.4 percent. Therefore, the signal observed so far does not allow claiming a first observation of astrophysical neutrinos but clearly points to IceCube as the place to look for them.

Inspired by the observation of these two PeV events, IceCube researchers are already working on an analysis with an optimized technique that will be substantially more sensitive to similar events at lower energies. Results of that analysis are expected soon and could provide more evidence of what is now a very intriguing hint of an astrophysical signal.