Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking
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Springer
Received: May 20, Revised: July 1, Accepted: July 13, Published: August 19,
2020 2020 2020 2020
The ATLAS collaboration E-mail: [email protected] Abstract: The factor of four increase in the LHC luminosity, from 0.5 × 1034 cm−2 s−1 to 2.0 × 1034 cm−2 s−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. Keywords: Hadron-Hadron scattering (experiments) ArXiv ePrint: 2005.09554
Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP08(2020)080
JHEP08(2020)080
Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking
Contents 1
2 ATLAS detector
3
miss trigger algorithms 3 Description of the ET 3.1 Level-1 trigger 3.2 Trigger using calorimeter cell signals (cell) 3.3 Trigger using topological clusters of calorimeter cells (tc lcw) 3.4 Trigger based on jets (mht) 3.5 Trigger implementing local pile-up suppression (pufit)
4 5 6 6 6 7
miss reconstruction 4 Offline object and ET
7
miss trigger performance 5 ET 5.1 Background model based on detector resolution 5.2 Level-1 trigger performance 5.3 High-level trigger performance 5.4 Trigger menu evolution and performance 5.5 Algorithm computation times 5.6 Dependence on event characteristics 5.7 Comparison with Monte Carlo simulation
8 8 11 12 16 18 19 21
6 Conclusion
23
A Full definition of the trigger implementing local pile-up suppression
24
B Details of the offline reconstruction algorithms
27
miss background distribution model C The cell ET
28
The ATLAS collaboration
35
1
Introduction
The trigger system [1] of the ATLAS experiment [2] is responsible for deciding which proton-proton (pp) bunch-crossing events are kept for later analysis. Storage and processing requirements limit the fraction of events that can be retained to the order of 10 −5 , with the rest being discarded and hence unavailable for further physics analysis.
–1–
JHEP08(2020)080
1 Introduction
–2–
JHEP08(2020)080
Particles that interact via neither the strong nor the electromagnetic force, and that escape the experiment without decaying, leave no visible signature. Efficient trigger selection of events that contain such invisible particles is
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