Does the neutrino feature change at night?

Does the neutrino feature change at night?

Scientists in the order of the working hypothesis announced an amazing observation, which was made with the help of the neutrino detector “SuperKamiokande”. Analysis of the information collected over the past 18 years shows that neutrinos produced as a result of nuclear reactions in the core of the Sun change their feature, reaching the unlighted side of the Earth.

Neutrinos are the “ghosts” of the quantum world that have no electric charge. Their mass is extremely small, and they move at the speed of light. Neutrinos interact so weakly with matter that they can pass through a whole planet from one edge to the opposite, without colliding with anything. They are only capable of weak nuclear interaction.

Although it would seem that such features of the particle make its tracking impossible, physicists have developed means to record direct collisions of the invisible neutrino with terrestrial matter.

In the case of the SuperKamiokande detector, a huge mine, located under a mountain 300 kilometers from Tokyo, was filled with 50,000 tons of ultrapure water, and thousands of detectors were placed on the walls of the mine. Occasionally, when a direct collision of a neutrino and a water molecule occurs, a high-energy electron or muon is formed. As a result of particle collisions, the Vavilov – Cherenkov effect arises. It is this short flash of electromagnetic radiation that is fixed by the sensors. If there is a sufficiently large capacity with water, it is statistically probable that the number of recorded collisions will be sufficient to create a kind of “neutrino telescope” (although, from a technical point of view, this will be largely not a telescope but a particle detector). Despite the fact that in the universe these neutral particles are abundant, in our region of the cosmos the main source of neutrinos is the sun.

There are three different types of neutrinos that differ in their properties: electron, tau, and muon. Due to the bizarreness of the quantum world, neutrinos can oscillate, moving from one type to another. The nature of such an oscillation for decades has been the subject of numerous studies in the field of nuclear physics.

The most surprising fact about neutrino flavors is that “SuperKamiokande” is able to capture only electron neutrinos. For a long time, it remained a mystery why there are much fewer solar neutrinos in the field of view of the detector than the scientific model predicts. It turns out that electron neutrinos (the presence of which devices are able to register) on their way through the interplanetary space oscillate in muon and tau neutrinos (which cannot be detected), which explains the discrepancies in numbers.

Scientists say that about half of the electron neutrinos, whose energy is 2 MeV and less, change their peculiarity without reaching the Earth. Higher-energy neutrinos oscillate even more often. The tendency is that the higher the neutrino energy, the less likely the particle will be detected. Such a strange behavior of the neutrino is called the “Mikheev-Smirnov-Wolfenstein effect”. It was discovered in 1986 by Soviet physicists Stanislav Mikheev and Alexei Smirnov, who conducted research based on the works of the American theorist Lincoln Wolfenstein from 1978. The MRV effect also suggests that oscillations occur in the opposite direction. When muon and tau neutrinos move through our planet, they can interact with electrons in the composition of dense earth matter. As a result, neutrinos can return to electronic type. And it seems that the detector “SuperKamiokande” managed to fix this effect in action.

After analyzing all the data collected during 18 years of observations, physicists noticed that during the nighttime the number of detected neutrinos increased by 3, 2%. When the side of the Earth where the detector is located is not illuminated by the sun, the particles must pass through the planet before they get into its field of view. In the afternoon, solar neutrinos reach the detector immediately after they cover a certain distance in space (and 10-15 km of the atmosphere). Everything indicates that when passing through our planet muon and tau neutrinos are affected by the effect of the MW.

Nevertheless, the researchers urge not to make too loud statements. The statistical significance of such conclusions does not allow one to call them a discovery, nor does it give grounds to consider them the ultimate proof that the effects of the MW are subject to the neutrino effect. The statistical significance of the research results is 2.7σ - that is, they are of interest to the scientific community, but they cannot be considered a discovery. One can speak about discovery only when the indicator of statistical significance reaches 5σ. It seems that in order to achieve such a coefficient, we need a larger detector. Fortunately, the construction of “HyperKamiokande” is already planned, which may even be able to use changes in neutrino odors to measure the density of rock.

The “HyperKamiokande” neutrino detector will be 25 times larger than the “SuperKamiokande”, which will allow us to get much more data, ”said David Wark, a neutrino analyst from Oxford University (who did not participate in this study). “I’m not sure that its size will be enough to measure the density of various layers of the Earth with an accuracy of interest to science, but in any case we will work in this direction.”

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