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OPERA experiment

The OPERA experiment (Oscillation Project with Emulsion-tRacking Apparatus) has been designed to perform a 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 Super Proton Synchrotron 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 oscillation of muon neutrinos during their 3 millisecond travel from Geneva to Gran Sasso. In OPERA, taus resulting from the interaction of tau neutrinos will be observed in "bricks" of photographic emulsion films interleaved with lead plates. The apparatus contains about 150 thousand of such bricks for a total mass of 1300 tons and is complemented by electronic detectors (trackers and spectrometers) and ancillary infrastructure. Its construction was completed in the spring of 2008 and the experiment is currently collecting data. On May 31, 2010, OPERA Researchers announced the first direct observation of a tau particle in a muon neutrino beam.

Neutrino beam

OPERA needs an intense and energetic beam of muon neutrinos traveling a distance of hundreds of kilometers to detect the appearance of oscillated tau neutrinos. A beam of this type is generated by collisions of accelerated protons with a graphite target after focusing the particles produced (pions and kaons in particular) in the desired direction. The products of their decays, muons and neutrinos, continue to travel in generally the same direction as the parent particle. Muon neutrinos produced in this way at CERN cross the earth crust reaching OPERA after a 732 km journey. This facility (CNGS: "CERN Neutrinos to Gran Sasso") has been built at CERN between 2000 and 2005 and it started operation in summer 2006.


OPERA is located in the Hall C of the Gran Sasso underground labs. Construction started in 2003, and the apparatus was completed in summer 2008. In OPERA, the taus resulting from the interaction of tau neutrinos will be observed in "bricks" of photographic films ("nuclear emulsion") interleaved with lead sheets. Each brick has an approximate weight of 8.3 kg and the two OPERA targets contain about 150,000 bricks arranged into parallel walls and interleaved with plastic scintillator counters. Each target is followed by a magnetic spectrometer for momentum and charge identification of penetrating particles. During the data collection, a neutrino interaction is tagged in real time by the scintillators and the spectrometers, which also provide the location of the bricks where the neutrino interaction occurred. These bricks are extracted from the walls asynchronously with respect to the beam to allow for film development, scanning and for the topological and kinematic search of tau decays.

Coordinates: 42.46°N 13.57°E

External links

Opera Main Page
CNGS Neutrino beam at CERN

List of neutrino experiments

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