Animated Z --> e+ + e- decay

This is what a typical Z --> e+ + e- 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 according to Einstein's famous formula E=mc2. The Z particle exists for just a fleeting moment before decaying into an electron and a positron.
The electron and the positron are charged particles and therefore leave behind a track of ionization in the main tracking detector.

The electron and the positron are then recognized by the fact that they interact very strongly in the electromagnetic calorimeter and actually stop there depositing all their energy. The energy deposit can be seen as a large blob of ionization in the calorimeter.

In Z decays to electron-positron pairs, the electron and the positron are usually the only particles produced.