"OPERA was built mostly to detect the appearance of tau neutrinos from a beam of muon neutrinos, a phenomenon called “oscillation” that enables one type of neutrinos to mutate into a completely different type when travelling over a large distance. This is something that had never been observed directly before but OPERA spotted one such event last year. To do so, they need to correlate the appearance of tau neutrinos in their detector with the arrival of muon neutrinos sent from CERN. Obviously, getting the timing right was essential, hence their careful checks on the arrival time of the muon neutrinos in Gran Sasso.And there, surprise! The neutrinos reached the Gran Sasso laboratory 60 nanoseconds (i.e. 60 billionth of a second) faster than light travelling over the same distance, even though neutrinos are expected to travel slightly below the speed of light."
