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 3 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.
About the OPERA Experiment
editNeutrinos Beam
editOPERA needs an intense and energetic beam of muon neutrinos traveling a distance of hundreds of kilometers to seek for the appearance of oscillated tau neutrinos. A beam of this type is generated from collisions of accelerated protons with a graphite target after focussing 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
The Detector
editOPERA is located in the Hall C of the Gran Sasso underground labs. its construction started in 2003 and the apparatus has been completed in summer 2008. In OPERA, the tau leptons 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 150000 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 taking, 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.