The CMS trigger system

David Newbold, the CMS Collaboration, Sudarshan Paramesvaran, Jim J Brooke

Research output: Contribution to journalArticle (Academic Journal)peer-review

421 Citations (Scopus)
257 Downloads (Pure)


This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing detector signals consistent with an electron, photon, muon, tau lepton, jet, or missing transverse energy. A programmable menu of up to 128 object-based algorithms is used to select events for subsequent processing. The trigger thresholds are adjusted to the LHC instantaneous luminosity during data taking in order to restrict the output rate to 100 kHz, the upper limit imposed by the CMS readout electronics. The second level, implemented in software, further refines the purity of the output stream, selecting an average rate of 400 Hz for offline event storage. The objectives, strategy and performance of the trigger system during the LHC Run 1 are described.
Original languageEnglish
Article numberP01020
Number of pages122
JournalJournal of Instrumentation
Issue number1
Publication statusPublished - 24 Jan 2017

Bibliographical note

Replaced with the published version. Added the journal reference and DOI. All the figures and tables can be found at


  • physics.ins-det
  • hep-ex


Dive into the research topics of 'The CMS trigger system'. Together they form a unique fingerprint.

Cite this