Animated Z --> quark + antiquark decay

This is what a typical Z --> quark + antiquark decay might look like. An electron coming in from the right collides with an anti-electron, a positron, coming in from the left. They annihilate and produce a Z particle, which decays into a quark and an antiquark.
The quark and the antiquark can't exist as free particles. Instead the energy in the strong interaction, that tries to hold them together as they fly apart, transforms into more new quarks. The quarks quickly combine into particles of two or three quarks, hadrons, which come out as showers or "jets" from the collision point. You will learn more about this in the second project.

It is very easy to recognize events in which the Z particle decays into quarks. You will see many particles coming out on either side interacting in the tracking chambers and the calorimeters. Sometimes, there are more than two jets of particles as you will see.

Remember that there can be electrons, positrons, and muons together with the hadrons in the jets. However, these are secondary particles. What we are interested in are the two primary particles produced when the Z decays, and if there are many hadrons in the event, it can only be a Z decay into quarks.