The ATLAS Jet Trigger for LHC Run 2

Abstract

The new centre of mass energy and high luminosity conditions expected for Run 2 at the Large Hadron Collider impose more demanding constraints on the ATLAS online trigger than ever before. An immense rate of proton-proton collisions must be reduced from the bunch-crossing rate of 40 MHz to approximately 1 kHz before data can be written on disk for offline analysis. The ATLAS trigger system performs real-time reconstruction and selection of these events in order to achieve this reduction. The selection of events containing jets is uniquely challenging at a hadron collider where nearly every event contains significant hadronic activity. It is, however, of crucial importance to exploit the incoming data in many physics topics in the new kinematic regime, ranging from early Standard Model measurements to searches for New Physics. Following the very successful first LHC run in 2010/12, the ATLAS trigger was much improved, including a new hardware at Level 1 and the restructuring of the High Level Trigger system, which merges two previously separated software-based processing levels. After summarising the design choices used in the jet trigger for Run 2, expected capabilities will be reviewed. The expected performance of upgraded jet trigger will be described and compared with the first trigger performance results from initial Run 2 data.