The ATLAS Trigger Algorithms Upgrade and Performance in Run-2

Understand

The ATLAS trigger has been used very successfully for the online event selection during the first part of the second LHC run (Run-2) in 2015/16 at a center-of-mass energy of 13 TeV.

• The trigger system is composed of a hardware Level-1 trigger and a software-based high-level trigger; it reduces the event rate from the bunch-crossing rate of 40 MHz to an average recording rate of about 1 kHz.
• The excellent performance of the ATLAS trigger has been vital for the ATLAS physics program of Run-2, selecting interesting collision events for a wide variety of physics signatures with high efficiency.
• The trigger selection capabilities have been significantly improved compared to Run-1, in order to cope with the higher event rates and pile-up during Run-2.