Which Right Neutrino is Right?
At left, a left-spinning neutrino moves more slowly than the speed of light because it has mass. Figuratively speaking, to a person running at the same speed as the neutrino, the particle appears to be at rest, but is still spinning left-handedly. If the person speeds up and passes the particle, it appears to travel backward (at right on blackboard). From that perspective, the particle is spinning right-handedly.