Real Z --> quark + antiquark decays

(Explanations below the WIRED view) Your browser does not support Java.

Below is static picture of the event:


Zoom out until you see the entire event and switch on the electromagnetic calorimeter in the barrel ("EMCal" in the "Barrel"). It is very useful to have this detector on to orientate yourself. This event has two nice jets of particles giving rise to signals in all detectors. If you zoom in as much as possible on the collision point, you will see that the red jet has particles that come from a point a few millimetres away from the actual collision point. You may have to rotate a bit too to see this clearly. If you have read all the information about the DELPHI detector, you will know that this is actually due to b-quarks. In this event the Z particle decays into a b-quark and an anti-b-quark. In the green jet the b-quark then decays into, among other things, a muon. You can see the muon if you switch to the "End view".


This event has two narrow jets. Compared to the previous event there are few particles but they are more energetic. This can be seen by the fact that they are straighter and there is plenty of activity in the hadron calorimeter.


This event has three well separated jets. In the second project, you will find the explanation of the origin of the third jet. Notice that the third yet is weaker than the other two jets. It has fewer particles and deposits only a little energy in the electromagnetic calorimeter.


This event has very wide jets and as the particles have low energy they bend strongly in the magnetic field. It is difficult to judge whether this event has three or four jets. To find the number of jets it is important to look at the initial direction of the particles before they start bending in the magnetic field. Although the colours are helpful, sometimes they are not always correct. They are put there as a guide, but you should not simply decide on the number of jets by the number of colours! The software often over-estimats the number of jets. Moreover, it is more reliable to look primarily at the charged particles to identify the jets, you should ignore isolated neutral particles.