quality:corruption
Speed

Before neutrinos were found to oscillate, they were generally assumed to be massless, propagating at the speed of light (c). According to the theory of special relativity, the question of neutrino velocity is closely related to their mass: If neutrinos are massless, they must travel at the speed of light, and if they have mass they cannot reach the speed of light. Due to their tiny mass, the predicted speed is extremely close to the speed of light in all experiments, and current detectors are not sensitive to the expected difference.

Also, there are some Lorentz-violating variants of quantum gravity which might allow faster-than-light neutrinos. A comprehensive framework for Lorentz violations is the Standard-Model Extension (SME).

The first measurements of neutrino speed were made in the early 1980s using pulsed pion beams (produced by pulsed proton beams hitting a target). The pions decayed producing neutrinos, and the neutrino interactions observed within a time window in a detector at a distance were consistent with the speed of light. This measurement was repeated in 2007 using the MINOS detectors, which found the speed of 3 GeV neutrinos to be, at the 99% confidence level, in the range between 0.999 976 c and 1.000 126 c. The central value of 1.000 051 c is higher than the speed of light but, with uncertainty taken into account, is also consistent with a velocity of exactly c or slightly less. This measurement set an upper bound on the mass of the muon neutrino at 50 MeV with 99% confidence. After the detectors for the project were upgraded in 2012, MINOS refined their initial result and found agreement with the speed of light, with the difference in the arrival time of neutrinos and light of −0.0006% (±0.0012%).

A similar observation was made, on a much larger scale, with supernova 1987A (SN 1987A). Antineutrinos with an energy of 10 MeV from the supernova were detected within a time window that was consistent with the speed of light for the neutrinos. So far, all measurements of neutrino speed have been consistent with the speed of light.