Wing Sheung Chan

The Large Hadron Collider and the ATLAS detector 43 and tracking information from the ID is included when the HLT decisions are made. This enables the HLTs to take the transverse momenta of reconstructed physics objects as well as the overall topology of the event into account. The event rate is reduced to approximately 1 kHz by the HLTs. The data of the triggered events can then be compressed, transferred and permanently stored. The trigger selections can usually be characterised by the multiplicity, transverse momentum thresholds and isolation conditions of physics objects. Some trigger selections are prescaled, meaning that only a certain fraction of the events that meet the selection criteria are stored. This allows events which have features that are too common to still be sampled without overloading the system. These are typically events with only low-energy objects.