The Neutrino - An Elusive Beast

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The Neutrino - An Elusive Beast

An infinite number of neutrinos shoot across the earth's surface every second, radiated by distant stars, and yet it has taken up until the mid 20th century for anyone to realize it. Finding neutrinos in your own backyard is easy. All you need is a ten-ton vat of pure water, 13000 photomultiplier tubes, and $11 million dollars in research funding. More on that later, but first, it would help to know a little more about what you're hunting.

The neutrino is an elusive beast possessing neither mass nor charge. The only proof of its existence comes in measuring its recoil effect. In the cold heart of subatomic physics, beyond the protons and neutrons that until recently served as the basic building block of atoms, a wellspring of subnuclear particles have been discovered in recent years. This much-theorized-upon neutrino is one of these particles. Research has discovered three types of neutrinos: the electron neutrino, the tau neutrino, and the muon neutrino. An anti-neutrino particle has also been discovered. All are created as the result of particle decay.

Neutrinos, born of decay, are given off as one particle deteriorates into a more stable state. Neutrinos are emitted in positron (another type of subnuclear particle) beta decay while the anti-neutrino is emitted from electron beta decay. As a pion decays into a muon, the muon neutrino emerges along side the muon. When a pion decays, a neutral particle must be emitted in the direction opposite that of the muon in order to conserve momentum. The original assumption was that this particle was the neutrino that conserves momentum in beta decay. In 1962, however, researchers proved that the neutrino accompanying pion decay is different. At t...

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...r for the population at large-- make our teeth whiter and cereal flakes stay crunchy in milk -- or is this just science for science's own sake. What's the payback for looking for neutrinos?

"Bah!" quips Super-K technician R.J. Wilkes, when asked if neutrino research is a big waste of time. He cites that the neutrino discoveries have opened new doors in astrophysics. Understanding neutrinos means a better understanding of nuclear reactions of stars, as in the explosion of SN1987A.

Works Cited:

"Detection of the Free Neutrino: A Confirmation", C.L. Cowan, Jr.,F. Reines, F.B. Harrison, H.W. Kruses and A.D. McGuire, Science 124, 103 (1956).

"40 Years of Neutrino Physics", Frederick Reines, Progress of Particle and Nuclear Physics, Vol. 32, 1 (1994).


The University of Washington's Super Kariokande Info Page

UC Irvine Physics Department

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