Many of you, learning of the OPERA experiment’s claim (whose plausibility is dropping rapidly) of maybe-faster-than-light neutrinos, may have wondered (a) how do physicists know so much about neutrinos, and (b) what was the OPERA experiment originally designed to do? [Hint: Only as a side project did the OPERA experiment set out to measure the speed of the neutrinos, and that’s why its design was by no means ideal for that purpose. ]
I’ve written an article that tries to explain the answer. It describes how there are multiple ways to classify neutrinos that are mutually exclusive, and this leads to a strange, and scientifically crucial, quantum effect called “neutrino oscillations.” After you’ve read the article, I hope you’ll have the language to understand this description of what the OPERA experiment was originally designed to do: Its original goal was to study a particular effect of neutrino oscillations, by sending muon-neutrinos traveling through the earth for 730 kilometers, oscillating as they go, and emerging in OPERA as a mixture of mainly muon neutrinos and tau neutrinos; then, any one of them colliding with an atomic nucleus might be converted either into a muon or a tau, an effect that OPERA would observe. [Recall that the three charged leptons in nature are electrons, muons and taus, with taus the heaviest.] The presence of taus as well as muons would confirm oscillations occur in the way most neutrino physicists currently believe that they do, and the rate of tau production would provide more precise information on neutrinos’ properties.
You’ll also understand something else important and relevant for OPERA: if you mess around with neutrino speeds even a tiny bit, you can easily run into conflicts with a wide variety of neutrino oscillation experiments. If that sounds cryptic, read the article!