Performance of the ATLAS trigger system in 2010

IEEE Transactions on Nuclear Science, 2000

IEEE Transactions on Nuclear Science, 2000

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in©¨collisions at 14 TeV center-of-mass energy, whilst rejecting the enormous number of background events. The High-Level Trigger (HLT = second level trigger and Event Filter), which is a software based trigger will need to reduce the level-1 output rate of kHz to Hz written out to mass storage. In this talk an overview of the current physics and system performance of the HLT selection for electrons and photons is given. The performance has been evaluated using Monte Carlo simulations and has been partly demonstrated in the ATLAS testbeam in 2004. The efficiency for the signal channels, the rate expected for the selection, the global data preparation and execution times will be highlighted. Furthermore, some physics examples will be discussed to demonstrate that the triggers are well adapted for the physics programme envisaged at the LHC.

Proceedings of The Eighth Annual Conference on Large Hadron Collider Physics — PoS(LHCP2020), 2020

The design and performance of the inner detector trigger for the high level trigger of the ATLAS experiment at the Large Hadron Collider during the 2016-2018 data taking period is discussed. In 2016, 2017, and 2018 the ATLAS detector recorded 35.6 fb -1 , 46.9 fb -1 , and 60.6 fb -1 respectively of proton-proton collision data at a centre-of-mass energy of 13 TeV. In order to deal with the very high interaction multiplicities per bunch crossing expected with the 13 TeV collisions the inner detector trigger was redesigned during the long shutdown of the Large Hadron Collider from 2013 until 2015. An overview of these developments is provided and the performance of the tracking in the trigger for the muon, electron, tau and b-jet signatures is discussed. The high performance of the inner detector trigger with these extreme interaction multiplicities demonstrates how the inner detector tracking continues to lie at the heart of the trigger performance and is essential in enabling the ATLAS physics programme.

IEEE Transactions on Nuclear Science, 2000

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in pp collisions at 14 TeV center of mass energy, while rejecting the enormous number of background events, stemming from an interaction rate of up to 10 9 Hz. The First Level trigger will reduce this rate to around O(100 kHz). Subsequently, the High Level Trigger (HLT), which is comprised of the Second Level trigger and the Event Filter, will need to further reduce this rate by a factor of O(10 3 ). The HLT selection is software based and will be implemented on commercial CPUs, using a common framework built on the standard ATLAS object oriented software architecture. In this paper an overview of the current implementation of the selection for electrons and photons *

The new Large Hadron Collider centre of mass energy and expected high luminosity conditions impose more demanding constraints on the ATLAS online trigger than ever before. The immense rate of proton-proton collisions must be reduced from the bunch-crossing rate of 40 MHz to approximately 1 kHz before the data can be written to 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 extremely challenging at a hadron collider where nearly every event contains significant hadronic activity. It is, however, of crucial importance for several physics analyses, including early searches for new physics in the new kinematic regime. Following the very successful first Large Hadron Collider run in 2010-12, the ATLAS Trigger has been upgraded, to include a new hardware topological module and a restructured High Level Trigger system, merging the two previous software-based processing levels. After summarising the overall performance of the jet trigger during the first Large Hadron Collider run, the software design choices and use of the topological module will be reviewed. The expected performance of jet trigger for the second LHC run is described and compared with the first trigger results from the Run 2 collisions data.

IEEE Transactions on Nuclear Science, 2003

The ATLAS trigger reduces the rate of interesting events to be recorded for off-line analysis in three successive levels from 40 MHz to 100 kHz, 2 kHz and 200 Hz. The high level triggers and data acquisition system are designed to profit from commodity computing and networking components to achieve the required performance. In this paper, we discuss data flow aspects of the design of the second level trigger (LVL2) and present results of performance measurements.

2008

Abstract The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton-proton collisions from beams crossing at 40 MHz. A three-level trigger system will select potentially interesting events in order to reduce the read-out rate to about 200 Hz. The first trigger level is implemented in custom-built electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of to less than 100 kHz.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007

The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton-proton collisions from beams crossing at 40 MHz. At the design luminosity of 10 34 cm −2 s −1 there are on average 23 collisions per bunch crossing. A threelevel trigger system will select potentially interesting events in order to reduce the read-out rate to about 200 Hz. The first trigger level is implemented in custombuilt electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of 10 4 to less than 100 kHz. The other two consecutive trigger levels are in software and run on PC farms. We present an overview of the first-level trigger system and report on the current installation status. Moreover, we show analysis results of cosmic-ray data recorded in situ at the ATLAS experimental site with final or close-to-final hardware.

Journal of High Energy Physics

The factor of four increase in the LHC luminosity, from 0.5 × 1034 cm−2s−1 to 2.0 × 1034cm−2s−1, and the corresponding increase in pile-up collisions during the 2015–2018 data-taking period, presented a challenge for the ATLAS trigger, particularly for those algorithms that select events with missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achieved in earlier operations. A study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of > 98% for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits.