The neutrinos are created. This is done in a way that the direction it will travel is also known. Once created we know of no way to chage its direction or velocity.
Cheers OM.
So they know exactly when that neutrino comes into being, so to speak? To the nanosecond?
Sorry for harping on, I honestly haven't a clue about this, but I thought nothing could change a neutrinos direction or velocity and if they are to measure it's speed then they would have to know it's starting position. I'm amazed if they can do that.