OPERA experiment
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This article may be affected by a current event. Information in this article may change rapidly as the event progresses. |
The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) is an experiment to test the phenomenon of neutrino oscillations. It exploits CERN Neutrinos to Gran Sasso (CNGS), a high-intensity and high-energy beam of muon neutrinos produced at the CERN Super Proton Synchrotron in Geneva and pointing to the LNGS underground laboratory at Gran Sasso, 730 km (450 mi) away in central Italy. OPERA is located in Hall C of LNGS and 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. 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 150,000 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 spring 2008 and the experiment is currently collecting data.
On May 31, 2010, OPERA researchers announced the observation of a first tau neutrino candidate event in a muon neutrino beam.[1] In September 2011, OPERA garnered international attention when it claimed detection of muon neutrinos traveling faster than light – other physicists were skeptical about the observation.[2]
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[edit] 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 has been built at CERN between 2000 and 2005 and it started operation in summer 2006.
[edit] Detector
OPERA is located in Hall C of the Gran Sasso underground labs. Construction started in 2003, and the apparatus was completed in summer 2008. 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.
[edit] Claimed faster-than-light detection
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This section documents a current event. Information may change rapidly as the event progresses. |
On 22 September 2011, the OPERA Collaboration garnered international attention, both public and within the physics community, when they claimed that neutrinos had been observed travelling from CERN in Geneva to the OPERA detector at faster-than-light speed. The particles were measured arriving at the detector 60.7 nanoseconds prior to the time expected if they were travelling at lightspeed, with a margin of error of 10.1 nanoseconds (6.9 statistical, 7.4 systematic), a significance of 6-sigma.[3] In particle physics, the standard baseline for a discovery announcement is 5-sigma significance.[4] Previous experiments have not exceeded that threshold; for instance, in 2007 Fermilab's MINOS collaboration reported results measuring the flight-time of neutrinos yielding a speed exceeding that of light by 1.8 sigma.[5] Those measurements were consistent with neutrinos traveling at lightspeed.[6] Fermilab noted in reaction to the OPERA announcement that the detectors for the MINOS project are being upgraded, and new results are not expected until at least 2012.[5]
Coordinates: 42°28′N 13°34′E / 42.46°N 13.57°E
[edit] References
- ^ N. Agafonova et al. [ OPERA Collaboration ] (2010). "Observation of a first ντ candidate event in the OPERA experiment in the CNGS beam". Phys. Lett. B 691: 138–145. arXiv:1006.1623. Bibcode 2010PhLB..691..138A. doi:10.1016/j.physletb.2010.06.022.
- ^ Challenging Einstein is usually a losing venture (Associated Press, September 23, 2011)
- ^ http://static.arxiv.org/pdf/1109.4897.pdf
- ^ http://dx.doi.org/10.1126%2Fscience.289.5488.2260
- ^ a b http://www.fnal.gov/pub/today/
- ^ Overbye, Dennis (2011-09-22). "Tiny Neutrinos May Have Broken Cosmic Speed Limit". The New York Times. http://www.nytimes.com/2011/09/23/science/23speed.html. "That group found, although with less precision, that the neutrino speeds were consistent with the speed of light."
[edit] External links
- Opera Main Page
- CNGS Neutrino beam at CERN
- CERN: First Appearance Of Tau Neutrino
- The appearance of the tau-neutrino
- OPERA publications
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