Events in which an electron-positron pair are produced are fairly easy to identify. We see a back-to-back pair of high momentum tracks pointing at high energy clusters of energy in the electromagnetic calorimeter.
Here are a couple of example events.
The incoming beams of electrons and positrons travel in opposite directions along the axis of the cylindrical detector. (In this picture this corresponds to a line that is perpendicular to your computer screen and through the centre of the concentric circles.)
In the second example event the electrons strike the end-cap region of the detector.
Next take a look at some example events.
Back to general section on "How to Identify Events Containing a Particle-Antiparticle Pair".