Publication: Performance of the CMS high-level trigger during LHC Run 2

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The CERN LHC provided proton and heavy ion collisions during its Run 2 operation period from 2015 to 2018. Proton-protoncollisions reached a peak instantaneous luminosity of2.1× 10$^{34}$ cm$^{-2}$s$^{-1}$, twice the initial design value, at √(s)=13 TeV. The CMS experiment records a subset of the collisions for further processing as part of its online selection of data for physics analyses, using a two-level trigger system: the Level-1 trigger, implemented in custom-designed electronics, and the high-level trigger, a streamlined version of the offline reconstruction software running on a large computer farm. This paper presents the performance of the CMS high-level trigger system during LHC Run 2 for physics objects, such asleptons, jets, and missing transverse momentum, which meet the broadneeds of the CMS physics program and the challenge of the evolving LHC and detector conditions. Sophisticated algorithms that were originally used in offline reconstruction were deployed online. Highlights include a machine-learning tagging algorithm and a reconstruction algorithm for tau leptons that decayhadronically.