If the collimators are open and the beam passes through the detector, you can actually see a lot less than when you break the particle beam with your big block of Tungsten (the material that the collimators are made of).
So… here you see what we see when beam goes through our detector. Practically nothing, which is good as there are no collisions at the moment. The only thing that the beam can collide with is the few remaining gas atoms in the beam vacuum (no vacuum is perfect). These occasional beam gas with beam-collisions are much cleaner and what you’re looking at here is a muon flying along the beam (the collision probably actually was some time before the actual detector) and being detected by our muon detectors.
