 |
Run II Discovery |
|
The Discovery of the Tau Neutrino
Taking a Bite from DONUT 2000
What is Fermilab? - Run II Newscasts - Analyze the Data - Particle Physics Bibliography
News Flash 2000: The Tau Neutrino is Discovered at Fermilab
Just as there are three generations of quarks, there are three generations of leptons. Leptons are "light" particles, lacking the color charge associated with quarks and interacting via the electroweak force only. The first generation is made up of the electron and its partner, the electron neutrino. Electrons are, of course, found in the orbitals of atoms. The second generation is made up of muons and muon neutrinos. Muons are the cosmic ray particles that are constantly raining down on the surface of the earth due to nuclear reactions high in the atmosphere caused by energetic particles from space. The third generation is made of the much rarer tau and the tau neutrino. But the tau neutrino had never been observed—until now.
In 1997 the Tevatron was used to bombard a target with protons to produce an intense beam of neutrinos. This neutrino beam was directed toward the DONUT (Direct Observation of NU Tau) detector, made of layers of iron plates separated by emulsions, that is, by sheets of a sort of film for photographing tau leptons. Very rarely (once for every 1012 chances), a tau neutrino would collide with an iron nucleus in such a way as to produce a tau lepton, which the emulsion would record. After several years of data analysis at Nagoya University in Japan, four events were found that clearly came from the tau neutrino. The result: another triumph for Fermilab and for the Standard Model.
More About the Tau Neutrino - CNN Story on Tau Neutrino - Neutrinos and Neutrino Mass