June 5, 2023


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Their laboratory is the deepest in the world. They used it to detect an almost elusive signal

What are antineutrinos anyway? To answer this question, it would be helpful to start by explaining what neutrinos are. These are the so-called fundamental elementary particles in the Standard Model. Neutrinos are divided into electron, muon, and tau, and each of these types has its own antineutrino counterpart.

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Due to the fact that neutrinos have practically no mass, are devoid of charge and hardly interact with other particles, scientists know about them much less than we would like. To distinguish neutrinos from antineutrinos, researchers focus on the electron neutrino that appears next to the positron, while the electron antineutrino will be present with the electron.

Liquid-filled tanks lined with so-called photomultiplier tubes are used to detect the reverse beta decay that accompanies antineutrino interactions with protons. These tanks allow detection of the subtle glow of Cherenkov radiation, which is caused by the activity of very fast-moving particles.

The signals detected by scientists at the Sudbury Neutrino Observatory came from a nuclear reactor more than 240 kilometers away.

Scholars write about how it was used in the pages Physical review letters. Most importantly, antineutrinos are produced by nuclear reactors. And although many of them are formed, they are so low in energy that they are difficult to detect. Detection is carried out using a laboratory hidden at a depth of 2073 meters, that is, the already mentioned Sudbury Neutrino Observatory. Notably, this facility was built in a former nickel mine.

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Analyzes of data collected in previous years showed evidence of inverse beta decay. The optical energy generated by this process was 2.2 MeV, with available detectors usually having trouble detecting values ​​below 3 MeV. Fortunately, in this case, the instruments were more sensitive, and members of the research team estimated with a probability of 99.7% that the detected signal was emitted by antineutrinos. As for the sources of neutrinos that reach the Earth from space, they can be created, for example, on the Sun. In addition, it is formed as a result of the interaction of cosmic rays with the upper layers of our planet.

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We are intrigued by the possibility of using pure water to measure antineutrinos from reactors over such long distances. We put a lot of effort into extracting a few signals from the data collected over the 190 days. The end result is satisfactory. sums up Logan Lipanovsky of the University of California, Berkeley