Evolution of online algorithms in ATLAS and CMS in Run 2

TL;DR

This paper discusses the enhancements in online algorithms and trigger systems implemented by ATLAS and CMS during LHC Run 2 to handle increased collision energy and luminosity, ensuring efficient data collection for key physics signals.

Contribution

It introduces new trigger algorithms and infrastructure improvements that adapt to harsher conditions in Run 2, maintaining high physics efficiency.

Findings

Improved trigger algorithms for electrons, photons, muons, and hadronic states.

Enhanced online selection infrastructure for higher luminosity conditions.

Maintained data quality and efficiency despite increased collision rates.

Abstract

The Large Hadron Collider has entered a new era in Run 2, with centre-of-mass energy of 13 TeV and instantaneous luminosity reaching $\mathcal{L}_\textrm{inst} = 1.4\times$10$^{34}$ cm$^{-2}$ s$^{-1}$ for pp collisions. In order to cope with those harsher conditions, the ATLAS and CMS collaborations have improved their online selection infrastructure to keep a high efficiency for important physics processes - like W, Z and Higgs bosons in their leptonic and diphoton modes - whilst keeping the size of data stream compatible with the bandwidth and disk resources available. In this note, we describe some of the trigger improvements implemented for Run 2, including algorithms for selection of electrons, photons, muons and hadronic final states.