Abstract
ATLAS utilizes a two-level trigger system in Run-2 to reduce the bunch-crossing rate of 40 MHz to an average recording rate of about 1 kHz. Events are selected based on physics signatures such as presence of energetic leptons, photons, jets or large missing energy. Despite the limited time available for processing collision events, the trigger system is able to exploit topological information as well as multi-variate methods, for example for b-tagging or tau identification. The ATLAS trigger menu specifies which triggers are used during data taking and how much rate a given trigger is allocated. For 2018 data taking, the trigger selections and menus have been improved to handle expected luminosities above 2 × 1034 cm−2 s−1 and to ensure robustness in the presence of multiple interactions per bunch crossing (pile-up).
Highlights
The ATLAS detector is a multipurpose particle physics detector with nearly 4π coverage in solid angle around the collision point, and is described in detail in Ref. [1]
This is followed by a software-based trigger that reduces the rate of recorded events to 1 kHz on average
The coincidences allowed to reduce the rate by about 30% for the primary L1 muon trigger, with an efficiency loss below. Another improvement that was introduced in order to run efficiently at high luminosity was a new algorithm to select events with large missing transverse energy (ETmiss)
Summary
The ATLAS detector is a multipurpose particle physics detector with nearly 4π coverage in solid angle around the collision point, and is described in detail in Ref. [1]. The 2018 trigger menu was designed to record and provide data for analyses, maintaining the same online pT requirements, referred to as thresholds, as in previous years. This allowed to provide a consistent dataset despite the higher luminosity and the presence of an increased number of interactions per bunch crossing (pile-up). The design of the trigger menu is based on the following building blocks: Primary triggers, which are used for physics measurements, and typically run unprescaled. Alternative triggers, which run non-standard online reconstruction algorithms complementary to primary and/or support triggers. Calibration triggers, which are used for detector calibrations and often run at high rate but store very small-size events with only the relevant information from the detector needed for the calibrations
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