Neutrinos polar ‘quick change’

Experiments conducted at the South Pole have allowed us to study the transformation of neutrinos produced in the Earth’s North Pole before reaching the other end of the globe. It is a result that allows not only to observe these effects with more details, and unprecedented, but also to derive valuable clues on their physical properties. The results in Physical Review D.
A series of experiments conducted at the South Pole have allowed us to measure the physical properties of neutrinos, exotic particles of which we know very little yet. The findings, published in Physical Review D, suggest that a type of neutrinos created in the Earth’s North Pole, undergo quantum fluctuations as they pass through the Earth before reaching the IceCube detector located in the other end of the globe to the South Pole, a process that turns them into another type of neutrino. This allows to study these effects with more details, and unprecedented, with the objective of obtaining new clues on their physical properties.


Credit: IceCube Collaboration

Neutrinos are elusive particles, elusive, crossing anything in their path as they propagate from the most remote regions of the Universe. The Earth is constantly bombarded by billions of neutrinos and they rarely interact with matter. At the South Pole, is located a giant experiment, IceCube, which is able to detect a rare collision of atoms and neutrinos in the ice through a complex system of detectors. The neutrinos represent a class of particles among the most abundant that exist in nature. Their number far exceeds that of the atoms in the universe, and yet we still know very little about their properties. These particles have been created with the Big Bang and can be produced in the stars or during violent phenomena and high energy, such as supernova explosions. Physicists call neutrinos “ghost particles” because they do not interact with matter and pass undisturbed through any obstacles they encounter.
IceCube experiment involved researchers from 44 institutions in 12 countries. It is a huge particle detector located deep in the ice at the South Pole. The size of the detector, a cubic kilometer, is due to the fact that neutrinos interact very weakly with matter so they collide with atoms in the ice very rarely. When they end up colliding, charged particles are created, which emit radiation which in turn can be detected by the so-called Digital Optical Modules, special detectors are extremely sensitive.
“We have registered 35 neutrinos that most likely come from the most remote regions of space,” explains Jason Koskinen, head of the group working IceCube experiment at the Niels Bohr Institute, University of Copenhagen. “These neutrinos are very energetic and since did not interact during their trip before arriving at Earth, they carry the information from the depths of space. In addition to the rare cosmic neutrinos, here we observe neutrinos that are created in Earth’s atmosphere in order to study their physical properties. ” When particles (protons) of high energy, which are produced by violent phenomena, such as supernovae or quasars, hit the Earth’s atmosphere, it generates a strong emission of neutrinos that pass undisturbed through the planet. Neutrinos who trained at the North Pole in a straight line across the Earth, and only a small fraction hits the ice at the South Pole, where the detector IceCube logs collisions.
Neutrinos are very light and for many years it was believed that these particles do not have a real mass. Now, however, it is believed that there are three types of neutrinos (electron, muon and tau) each of which has a specific mass, which remains incredibly small, ie less than a millionth of the mass of the electron. “The neutrinos created in the atmosphere over the North Pole are mainly muon neutrinos. During their long journey into the Earth 13,000 km long, muon neutrinos undergo quantum fluctuations that turn them into another type of neutrino, tau neutrinos that is, before they are detected by IceCube other side of the globe. Now, we can study these effects with more details and unprecedented, and this allows us to get new clues about their physical properties, “continues Koskinen.
The researchers were able to study atmospheric neutrinos in the IceCube detector for a period of three years, analyzing 5,200 interactions between atmospheric neutrinos and atoms of the ice. “We have confirmed the fact that neutrinos undergo fluctuations, even at high levels of energy, and we have calculated the amount of these oscillations. In other words, we measured only the muon neutrinos and compared to the number that is produced in the atmosphere, only a fraction of them reaches the South Pole. The explanation is that the muon neutrinos undergo quantum fluctuations and are transformed into tau neutrinos: why we see less. If not would suffer this transformation, we would see them all. Therefore, our calculations indicate that at least 20 percent are subject to quantum effects as they pass through the Earth, “concludes Koskinen.

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