The "dim flash of light" is called Cherenkov radiation and there's directional information encoded in it. Depending on which (or when a?) particular detector sa

The "dim flash of light" is called Cherenkov radiation and there's directional information encoded in it. Depending on which (or when a?) particular detector saw that light, the direction of the incoming particle can be calculated. https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation