Performance of electron and photon triggers in ATLAS during LHC Run 2

Abstract

Abstract Electron and photon triggers covering transverse energies from 5 $$\text {GeV }$$ GeV to several $$\text {TeV }$$ TeV are essential for the ATLAS experiment to record signals for a wide variety of physics: from Standard Model processes to searches for new phenomena in both proton–proton and heavy-ion collisions. To cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), to $$2.1 \times 10^{34}\,\hbox {cm}^{-2}\hbox { s}^{-1}$$ 2.1 × 10 34 cm - 2 s - 1 , and a similar increase in the number of interactions per beam-crossing to about 60, trigger algorithms and selections were optimised to control the rates while retaining a high efficiency for physics analyses. For proton–proton collisions, the single-electron trigger efficiency relative to a single-electron offline selection is at least 75% for an offline electron of 31 $$\text {GeV }$$ GeV , and rises to 96% at 60 $$\text {GeV }$$ GeV ; the trigger efficiency of a 25 $$\text {GeV }$$ GeV leg of the primary diphoton trigger relative to a tight offline photon selection is more than 96% for an offline photon of 30 $$\text {GeV }$$ GeV . For heavy-ion collisions, the primary electron and photon trigger efficiencies relative to the corresponding standard offline selections are at least 84% and 95%, respectively, at 5 $$\text {GeV }$$ GeV above the corresponding trigger threshold.