Neutrino Particle Discovery
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Posted by Jim Down in Science section |
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Experiment includes 150 scientists, students from six countries
Washington – First results of a new experiment on neutrinos were announced March 30, 2006, by an international collaboration of scientists at the U.S. Department of Energy (DOE) Fermi National Accelerator Laboratory (Fermilab).
The experiment involved 150 scientists, engineers, technical specialists and students from 32 institutions in six countries, Brazil, France, Greece, Russia, the United Kingdom and the United States.
A neutrino is one of the fundamental particles that make up the universe, and scientists have been working since 1931 to prove its existence and, later, to understand its properties.
The abundance of neutrinos in the universe, produced by stars and nuclear processes, might explain how galaxies formed and why antimatter has disappeared. Ultimately, the elusive particles might explain the origin of the neutrons, protons and electrons that make up all the matter in the universe. One thing that is known about the neutrino is that, unlike particles such as electrons, muons and tau particles, it has no electrical charge. Three kinds, or flavors, of neutrinos exist, each related to a charged particle – the electron neutrino, the muon neutrino, and the tau neutrino.
Neutrinos are very hard to detect because they rarely interact with anything. They can pass easily through solid objects such as a planet, walls or even a human hand without leaving a trace of their existence.
THE EXPERIMENT
At Fermilab, during the Main Injector Neutrino Oscillation Search (MINOS) experiment, scientists sent a high-intensity beam of muon neutrinos from the lab’s site in Illinois to a particle detector in Minnesota, and observed the disappearance of a significant fraction of these neutrinos.
The observation is consistent with an effect known as neutrino oscillation, in which neutrinos change from one kind to another.
Most of the neutrinos traveling the 724 kilometers from Fermilab to Minnesota – straight through the Earth, no tunnel needed – leave no signal in the MINOS detector.
If neutrinos had no mass, the particles would not change as they travel through the Earth and the MINOS detector in Minnesota would have recorded about 177 muon neutrinos.
Instead, the MINOS collaboration found only 92 muon neutrino events – a clear observation of muon neutrino disappearance and hence neutrino mass.
In this scenario, muon neutrinos can turn into electron neutrinos or tau neutrinos, or it is possible that the neutrinos decayed. The MINOS collaboration will have to record much more data to find out exactly why the neutrinos are disappearing.
DOE provides the major share of the funding, with other funding from the U.S. National Science Foundation and the United Kingdom’s Particle Physics and Astronomy Research Council (PPARC).
“The MINOS experiment is a hugely important step in our quest to understand neutrinos – we have created neutrinos in the controlled environment of an accelerator and watched how they behave over very long distances,” said PPARC chief executive Keith Mason.
“This has told us that they are not totally massless as was once thought,” he added, “and opens the way for a detailed study of their properties.”
The Fermilab side of the MINOS experiment consists of a beam line in a 1,219-meter-long tunnel pointing from Fermilab to Minnesota. A neutrino detector 107 meters below the surface of the Fermilab site measures the composition and intensity of the neutrino beam as it leaves the lab.
The Minnesota side of the experiment features a huge 5,443-metric-ton particle detector that measures the properties of the neutrinos after their trip to northern Minnesota. The cavern housing the detector is 805 meters underground in a former iron mine.
Additional information and a press release about the MINOS experiment are available at the Fermilab Web site.
(Distributed by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)
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