Electron/positron events distinguish themselves by having (almost) always exactly two tracks which are clearly visible in the detector.

Since electrons and positrons (like most particles except for muons) get “caught” by the calorimeter, these tracks usually end there, which means that one can see a red energy deposition in the calorimeter. They can most easily be distringuished from muons by that fact that no or only very few green detector hits along the outer line are visible in the kaon-muon-calorimeter.

Since only the electron and the positron are produced and they don’t decay any further, these events usually have very little missing energy and high straightness.