Top Quarks and Leptons

When a top quark is produced, either in simulation or in reality, it immediately decays into lighter particles, which decay into even lighter particles as they fly through the detector, some of these particles deposit energy into the detector, and others pass through leaving no trace. Physicists must act as detectives, using the clues left in the detector to infer what actually happened in the initial collision, and the full set of particles that appeared in the aftermath. To detect top quarks, or any other massive particle produced within the ATLAS detector, it is necessary to create triggers that recognize signals from specific decay products. When a top quark decays the most likely result is a W boson and a bottom quark. These particles also decay quickly, so the trigger must recognize the products later on in the decay chain. The easiest signature to detect is when the W decays into either a muon, tau or electron, and its associated neutrino. These particles are called leptons.