Very odd rectangle pattern in tracker
by Whoandwhatitis moderator
There's a very tightly-bunched set of particles in the tracker at 220°. There is a lot of energy in the electromagnetic calorimeter in this area. The measured imbalance of energy is opposite this feature. Looks also like there were some photons very near the muons.
looks like a jet, just very tightly collimated. That might mean the "parent particle" decayed quite close to the TRT, giving the jet not much time to spread out, and/or that it had considerable transverse momentum, which the jet inherited again leading to not much spread. Since we can't see it in slice we don't know where it is relative to the collision point along the z axis, nor how much it fans out "lengthwise". The fact we see no tracks probably just means each individual one didn't have enough momentum to make the display cut, but may also have to do with distance from the beamline (if it decayed outside the silicon tracking cylinders; I dunno if that can lead to the computer "missing" them [but I doubt it]).
More than that would need A Scientist to weigh in 😃
google "lepton jet", and also check out image search for some interesting diversions about higgsino (supersymmetry) searches using particular patterns of light-jet detections.
The event displays shown in this project do not show tracks that point back very close to the collision point. This is done to focus attention on the tracks which may come from a displaced vertex but it makes it harder to interpret the tightly bunched hits seen here.
When we refer to a jet this normally means collimated particles originating from a quark, antiquark or gluon and these will originate very close to the collision point not further out in the detector.
Hope this helps.