Abstract
The ATLAS trigger system has been used very successfully for the online event selection during the LHC's first run (Run-1) between 2009 and 2013 at centre-of-mass energies (√s) between 900 GeV and 8 TeV. The trigger system consists of a hardware Level-1 (L1) and a software-based high-level trigger (HLT) that reduces the event rate from the design bunch-crossing rate of 40 MHz to an average recording rate of a few hundred Hz. During the next data-taking period (Run-2) starting in early 2015, the LHC will operate at √s = 13 TeV, resulting in roughly five times higher trigger rates.We will review the upgrades to the ATLAS trigger system that have been implemented during the long shutdown and that will allow us to cope with these increased trigger rates while maintaining or even improving our efficiencies to select relevant physics processes. These include changes to the L1 calorimeter trigger, the introduction of new L1 topological trigger modules, improvements in the L1 muon system and the merging of the previous two-level HLT system into a single event-filter farm. Finally, we will summarize the commissioning status of the trigger system in view of the imminent restart of data-taking.
Highlights
During the Run-1 period between 2009 and early 2013, the ATLAS trigger system [1√] operated very successfully
For Run-2, many new features were implemented in all the sub-systems. These proceedings describe the major upgrades that have been implemented in L1 calorimeter trigger system (L1Calo), L1 muon trigger system (L1Muon), L1 topological trigger modules (L1Topo) and the high-level trigger (HLT)
The ATLAS trigger system is considered to be ready for Run-2
Summary
During the Run-1 period between 2009 and early 2013, the ATLAS trigger system [1√] operated very successfully. The bunch spacing reduction from 50 ns to 25 ns, while helping to control the increase in in-time pile-up (interactions occurring in the same bunch-crossing as the collision of interest), will increase both the out-of-time pile-up (interactions occurring in bunch-crossings just before and after the collision of interest) and beam-induced fake trigger rates, in the muon system In these proceedings, a series of upgrades to the ATLAS trigger system for Run-2 [2] are reviewed. The trigger system consists of a hardware Level-1 (L1) and a single software-based high-level trigger (HLT) This new two-stage system will reduce the event rate from the bunch-crossing rate of 40 MHz to 100 kHz at L1 and to an average recording rate of 1 kHz at the HLT. These proceedings describe the major upgrades that have been implemented in L1Calo, L1Muon, L1Topo and the HLT
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