July 31, 2017 to August 4, 2017
Fermi National Accelerator Laboratory
US/Central timezone

The ATLAS Trigger algorithms upgrade and performance in Run 2 (TDAQ)

Jul 31, 2017, 2:38 PM
1 East (Fermi National Accelerator Laboratory)

1 East

Fermi National Accelerator Laboratory

Presentation Computing, Analysis Tools and Data Handling Computing, Analysis Tools, and Data Handling


Catrin Bernius (SLAC)


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 wide variety of physics signatures with high efficiency. The trigger selection capabilities of ATLAS during Run-2 have been significantly improved compared to Run-1, in order to cope with the higher event rates and pile-up which are the result of the almost doubling of the center-of-mass collision energy and the increase in the instantaneous luminosity of the LHC. At the Level-1 trigger the undertaken improvements resulted in more pile-up robust selection efficiencies and event rates and in a reduction of fake candidate particles. A new hardware system, designed to analyze event-topologies, supports a more refined event selection at the Level-1. A hardware-based high-rate track reconstruction, currently being commissioned, enables the software trigger to make use of tracking information at the full input rate. Together with a re-design of the high-level trigger to deploy more offline-like reconstruction techniques, these changes improve the performance of the trigger selection turn-on and efficiency to nearly that of the offline reconstruction. In order to prepare for the anticipated further luminosity increase of the LHC in 2017/18, improving the trigger performance remains an ongoing endeavor. Thereby coping with the large number of pile-up events is one of the most prominent challenges. This presentation gives a short review the ATLAS trigger system and its performance in 2015/16 before describing the significant improvements in selection sensitivity and pile-up robustness, which we implemented in preparation for the expected highest ever luminosities of the 2017/18 LHC.

Primary author

Evelyn Thomson (University of Pennsylvania)

Presentation materials