Faster-than-light neutrino anomaly
In 2011, the OPERA experiment mistakenly observed neutrinos appearing to travel faster than light. 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. OPERA scientists announced the results of the experiment in September 2011 with the stated intent of promoting further inquiry and debate. 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. The errors were first confirmed by OPERA after a ScienceInsider report; accounting for these two sources of error eliminated the faster-than-light results. 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. ICARUS used a partly different timing system from OPERA and measured seven different neutrinos. 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. 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. 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 July 12, 2012, OPERA updated their paper by including the new sources of errors in their calculations. They found agreement of neutrino speed with the speed of light. Neutrino speeds "consistent" with the speed of light are expected given the limited accuracy of experiments to date. Neutrinos have small but nonzero mass, and so special relativity predicts that they must propagate at speeds lower than that of light. 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. (Wikipedia).
