CERN: First Appearance Of Tau NeutrinoFirst appearance of a tau neutrino event in the OPERA detector at the Gran Sasso Laboratory, proving the neutrino oscillation from the muon type of the CERN beam to the tau type observed.
Particle Chameleon Caught in the act of Changing
Geneva 31 May 2010. Researchers on the OPERA experiment at the INFN1's Gran Sasso laboratory in Italy today announced the first direct observation of a tau particle in a muon neutrino beam sent through the Earth from CERN, 730km away. This is a significant result, providing the final missing piece of a puzzle that has been challenging science since the 1960s, and giving tantalizing hints of new physics to come.
The neutrino puzzle began with a pioneering and ultimately Nobel Prize winning experiment conducted by US scientist Ray Davis beginning in the 1960s. He observed far fewer neutrinos arriving at the Earth from the Sun than solar models predicted: either solar models were wrong, or something was happening to the neutrinos on their way. A possible solution to the puzzle was provided in 1969 by the theorists Bruno Pontecorvo and Vladimir Gribov, who first suggested that chameleon-like oscillatory changes between different types of neutrinos could be responsible for the apparent neutrino deficit.
Several experiments since have observed the disappearance of muon-neutrinos, confirming the oscillation hypothesis, but until now no observations of the appearance of a tau-neutrino in a pure muon-neutrino beam have been observed: this is the first time that the neutrino chameleon has been caught in the act of changing from muon-type to tau-type.
• http://press.web.cern.ch/press...ses/Releases2010/PR08.10E.html
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OPERA - Oscillation Project with Emulsion-tRacking Apparatus
The OPERA experiment has been designed to perform the most straightforward test of the phenomenon of neutrino oscillations. This experiment exploits the CNGS high-intensity and high-energy beam of muon neutrinos produced at the CERN SPS in Geneva pointing towards the LNGS underground laboratory at Gran Sasso, 730 km away in central Italy. OPERA is located in the Hall C of LNGS and it is aimed at detecting for the first time the appearance of tau-neutrinos from the transmutation (oscillation) of muon-neutrinos during their three millisecond travel from Geneva to Gran Sasso.
In OPERA, tau-leptons resulting from the interaction of tau-neutrinos will be observed in "bricks" of photographic emulsion films interleaved with lead plates. The apparatus contains about 150000 of such bricks for a total mass of 1300 tons and is complemented by electronic detectors (trackers and spectrometers) and ancillary infrastructure. Its construction has been completed in spring 2008 and the experiment is currently in data taking.
Neutrinos are elementary particles postulated by Pauli in the 30's as a "desperate attempt" to save the principle of energy conservation in radioactive beta decays. They have been observed 20 years later emerging from nuclear reactors and, since then, many of their physical properties have been established. There are three types, or "flavors", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos.
If the rest mass of the neutrinos is different from zero, transitions among different flavors can take place when they propagate through space ("neutrino oscillations"). OPERA is aimed at performing a straightforward test of this phenomenon, trying to identify uniquely the appearance of tau neutrinos from a pure muon-neutrino beam propagating from Geneve to Gran Sasso.
• http://operaweb.lngs.infn.it/
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