Cosmic Neutrinos Revealed by IceCube Observatory

The South-Pole-based IceCube Neutrino Observatory, at Amundsen-Scott Station, claims that it detected ultrahigh-energy neutrinos, coming from the Northern sky, which, together with the previous measures in the Southern hemisphere, become a strong confirmation about the possibility to collect neutrinos from powerful astrophysical accelerators outside our Galaxy.

Researchers, working at IceCube experiment, analyzed thoroughly billions of subatomic particles that annually pass through their detector. The goal was to look for new evidence supporting the existence of cosmic neutrinos, as suggested by a series of previous observations. This type of test is very important because it may mark the birth of a new form of Astronomy in the neutrino's field.

In the recent study, the detection of about twenty ultrahigh-energy muons (secondary particles, which are formed on very rare occasions, when neutrinos interact with other particles) provides an independent confirmation of cosmic neutrinos.

The observations were reported in an article, published on August 20, 2015 in the journal Physical Review Letters, that indicated the data as a "clear signal" in favor of cosmic neutrinos, ultrahigh-energy particles that passed through space without obstacles by stars, planets, galaxies, magnetic fields or clouds of interstellar dust.

Given that neutrinos have a very small mass and no electric charge, it is very difficult to detect them and they are observed only indirectly, when they collide with other particles by generating secondary particles such as muons.
Furthermore there are different types of neutrinos, created in different astrophysical processes. 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. The particles created during these events are accelerated to energy levels that exceed, by a factor of more than a million, energies reached in the most powerful terrestrial accelerators like the Large Hadron Collider.

These particles are very valuable to astrophysicists because the information are uncontaminated, despite the journeys long even millions of years to reach us. The study of ultrahigh-energy neutrinos could help to solve a number of open problems in Physics, including how are formed the most powerful particle accelerators in the universe.

IceCube consists of an array of 5160 optical sensors that dangle in a cubic kilometer of Antarctic ice.
The latest observations were made by pointing the detector IceCube towards the Earth's Northern sky. In this case, Earth functioned as a neutrino filter, by allowing to exclude, from the analysis, the muons created by the interaction between cosmic rays and the Earth's atmosphere.

In the analysis presented, a data sample of approximately 35 000 muon neutrinos from the Northern sky is extracted from data taken during 659.5 days of live time recorded between May 2010 and May 2012.
However, only about twenthy neutrinos showed energy levels that indicate cosmic sources. Precisely, the collaboration reports 21 neutrinos (predominantly muon neutrinos) with energies estimated to lie between 100 and 1700 tera-electron-volts.

The results are highly significant and open the door to a new era in particle physics, but, if on the one hand the new observations confirm the existence of cosmic neutrinos and the efficacy of IceCube, on the other hand the sources of high-energy neutrinos are still unidentified.

Paper: Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube
Synopsis on
M. G. Aartsen et al. (IceCube Collaboration)
Phys. Rev. Lett. 115, 081102 (2015)
Open access version in arXiv >>
Image explanation: representation of one among the 21 ultrahigh-energy neutrinos revealed by IceCube Observatory by aiming tools towards Northern hemisphere. The neutrino was observed on Oct. 28, 2010.
Credits: IceCube Collaboration

#astrophysics #particle_physics #IceCube_Collaboration #neutrinos #research #Universe
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