# Commissioning of the CMS High Level Trigger

## TL;DR

The paper details the commissioning and validation of the CMS High Level Trigger system, highlighting its architecture, operational readiness, and performance during initial LHC beam runs in 2008.

## Contribution

It provides a comprehensive overview of the CMS HLT system's functionalities, validation process, and operational experience during early LHC data collection.

## Key findings

- HLT system successfully validated with Monte Carlo data
- Operational during initial LHC beam runs in September 2008
- Demonstrated capability to handle high luminosity and data rates

## Abstract

The CMS experiment will collect data from the proton-proton collisions delivered by the Large Hadron Collider (LHC) at a centre-of-mass energy up to 14 TeV. The CMS trigger system is designed to cope with unprecedented luminosities and LHC bunch-crossing rates up to 40 MHz. The unique CMS trigger architecture only employs two trigger levels. The Level-1 trigger is implemented using custom electronics, while the High Level Trigger (HLT) is based on software algorithms running on a large cluster of commercial processors, the Event Filter Farm. We present the major functionalities of the CMS High Level Trigger system as of the starting of LHC beams operations in September 2008. The validation of the HLT system in the online environment with Monte Carlo simulated data and its commissioning during cosmic rays data taking campaigns are discussed in detail. We conclude with the description of the HLT operations with the first circulating LHC beams before the incident occurred the 19th September 2008.

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Source: https://tomesphere.com/paper/0908.1065