Riddles of the "disappeared" neutrinos

New neutrino oscillation results refute standard model

Neutrino detector Super-Kamiokande Super Kamiokande
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A team of nearly 100 physicists from all over the world has now confirmed for the first time that neutrinos, elementary particles that have so far hardly been researched, can transform from one neutrino to another as they travel through the earth. This finding suggests that the previous standard model of physics, which describes the fundamental forces and particles of matter, could be incomplete.

"The results show that the standard model needs to be changed to better explain the fundamental forces of matter, " explains James Stone, a physics professor at Harvard University. "You clear all other explanations of the table."

Stone and his associates are part of the Super-Kamiokande Collaboration, a project taking place in Japan, involving researchers from more than 30 institutions worldwide. The new analysis of the project focused on atmospheric neutrinos that arise when high-energy cosmic rays collide with the Earth's upper atmosphere. Neutrinos come in two "types": the electron type and the muon type.

Already in 1998, the Super K research group reported for the first time that neutrinos oscillate. The discovery came from the observation that the number of muon neutrinos that reached the subterranean detector only after passing through the earth was significantly less than the number of those who took the "short" path from the top through the atmosphere into the ground, At the same time, the data showed that the muon neutrino can transform into a third neutrino variety, the tau neutrino, that does not arise in cosmic collisions.

The probability of such a change follows a certain pattern, the so-called oscillation. Theoretically, however, such a grade change can only take place when neutrinos have a mass - which they do not do according to the previous standard model. Although the discovery of 1998 had already revealed the first indications of gaps in the standard model, physicists could not provide a clear explanation for this phenomenon. They postulated that the neutrinos on their way through the earth apparently get lost because they transform into other particles, but did not consider the conversion into another neutrino type. display

The new results indicate that these assumptions are inaccurate and do not fit the observed oscillation pattern. In addition, the measurements clearly show for the first time that there are mass differences between the neutrinos and are at the same time the most accurate mass measurements ever made on neutrinos.

(Boston University, 12.07.2004 - NPO)