PhysOrg - General Physics - 31 May 2010
More information: The OPERA experimentAfter seven years since the start of construction of the OPERA experiment and three years of operation in the underground Gran Sasso Laboratory of the Italian National Institute of Nuclear Physics (INFN), one of the many billions of muon-neutrinos produced at the CERN accelerator complex (CNGS) has likely "transformed" into a tau-neutrino that has been observed by the OPERA apparatus.
This is an extremely important result. The observation of a few more of these tau-neutrino events over a large number of conventional muon-neutrino interactions will represent the long awaited proof of the direct conversion of one type of neutrino into another: the so called "neutrino oscillation" mechanism.
The disappearance of the initial neutrino flavour has already been observed by several experiments in the last 15 years, but the "direct appearance" is still the outstanding missing tile of the puzzle, and the OPERA experiment is unique worldwide for this purpose. Neutrino oscillation is today the only indication of new, fascinating physics beyond the so-called Standard Model of particles and interactions, opening the possibility of unexpected implications in cosmology, astrophysics and particle physics.
The experiment was inaugurated in 2006, when the first "normal" muonneutrinos were detected after a trip of 730 km from CERN, covered in about 2.4 milliseconds, at the speed of light. After then, a careful and tireless search started to find the tiny and very special signal induced by a tau-neutrino.
Particle Chameleon Caught in the Act of Changing
Science Daily - 31 May 2010
Researchers on the OPERA experiment at the INFN'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, 730 km 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.