What is it
What does the green rectangle in the outer bands signify along with the yellow in the green band yet nothing in the red band and no track?
by Whoandwhatitis moderator
The green band in the muon detector (blue ring) is a measure of the amount of energy at that particular location. This is mentioned in the FAQ:
The green band is the electromagnetic calorimeter and indicates a number of particles. As mentioned in the following discussion, it could be a photon (or electron, and possibly other leptons):
As you say, the object at the bottom of this image has left lots of energy in the electromagnetic calorimeter layer (green), but has not track. This is the characteristic signature of a photon (i.e. particle of light).
So it's very likely (from my limited experience) that multiple particles are contributing to what you see in the same approximate location on the two detectors. This image should help visualize what's going on here: