![]() In a March 2011 analysis of their data, scientists of the OPERA collaboration reported evidence that neutrinos they produced at CERN in Geneva and recorded at the OPERA detector at Gran Sasso, Italy, had traveled faster than light. The OPERA collaboration stated in their initial press release that further scrutiny and independent tests were necessary to definitely confirm or refute the results. This eliminated some possible errors related to matching detected neutrinos to their creation time. In a two-week span up to November 6, the OPERA team repeated the measurement with a different way of generating neutrinos, which helped measure travel time of each detected neutrino separately. As computed, the neutrinos' average time of flight turned out to be less than what light would need to travel the same distance in a vacuum. OPERA researchers used common-view GPS, derived from standard GPS, to measure the times and place coordinates at which the neutrinos were created and detected. The experiment created a form of neutrinos, muon neutrinos, at CERN's older SPS accelerator, on the Franco–Swiss border, and detected them at the LNGS lab in Gran Sasso, Italy. 6 Discussions within the OPERA collaboration.Nonetheless, known neutrino production processes impart energies far higher than the neutrino mass scale, and so almost all neutrinos are ultrarelativistic, propagating at speeds very close to that of light. Neutrinos have small but nonzero mass, and so special relativity predicts that they must propagate at speeds lower than that of light. Neutrino speeds "consistent" with the speed of light are expected given the limited accuracy of experiments to date. They found agreement of neutrino speed with the speed of light. On July 12, 2012, OPERA updated their paper by including the new sources of errors in their calculations. The press release, made from the 25th International Conference on Neutrino Physics and Astrophysics in Kyoto, states that the original OPERA results were wrong, due to equipment failures. On June 8, 2012, CERN research director Sergio Bertolucci declared on behalf of the four Gran Sasso teams, including OPERA, that the speed of neutrinos is consistent with that of light. In addition, the Gran Sasso experiments BOREXINO, ICARUS, LVD and OPERA all measured neutrino velocity with a short-pulsed beam in May, and obtained agreement with the speed of light. ICARUS used a partly different timing system from OPERA and measured seven different neutrinos. In March 2012, the co-located ICARUS experiment reported neutrino velocities consistent with the speed of light in the same short-pulse beam OPERA had measured in November 2011. The errors were first confirmed by OPERA after a ScienceInsider report accounting for these two sources of error eliminated the faster-than-light results. Later the team reported two flaws in their equipment set-up that had caused errors far outside their original confidence interval: a fiber optic cable attached improperly, which caused the apparently faster-than-light measurements, and a clock oscillator ticking too fast. OPERA scientists announced the results of the experiment in September 2011 with the stated intent of promoting further inquiry and debate. Even before the source of the error was discovered, the result was considered anomalous because speeds higher than that of light in a vacuum are generally thought to violate special relativity, a cornerstone of the modern understanding of physics for over a century. In 2011, the OPERA experiment mistakenly observed neutrinos appearing to travel faster than light. Only the PolaRx GPS receiver is above-ground, and fiber cables bring the time underground. At the top are the GPS satellites providing a common clock to both sites, making time comparison possible. The left waveform is the measured distribution of protons, and the right that of the detected OPERA neutrinos. The red lines are the CERN Neutrinos to Gran Sasso (CNGS) beam to the LNGS lab where the OPERA detector is. It passes the beam current transformer (BCT), hits the target, creating first, pions and then, somewhere in the decay tunnel, neutrinos. Leftmost is the proton beam from the CERN SPS accelerator.
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