The CMS High Level Trigger

TL;DR

This paper describes the design and performance of the CMS High Level Trigger system at CERN, which reduces the data rate from the LHC's proton collisions through hardware and software triggers, enabling efficient data collection for physics analysis.

Contribution

It provides a detailed overview of the CMS HLT algorithms, expected trigger rates, and performance metrics, highlighting the system's effectiveness in real-time event selection.

Findings

Effective reduction of data rate by a factor of 10^6

High physics efficiency maintained at high trigger rates

Detailed performance analysis of trigger algorithms

Abstract

At the Large Hadron Collider at CERN the proton bunches cross at a rate of 40MHz. At the Compact Muon Solenoid experiment the original collision rate is reduced by a factor of O (1000) using a Level-1 hardware trigger. A subsequent factor of O(1000) data reduction is obtained by a software-implemented High Level Trigger (HLT) selection that is executed on a multi-processor farm. In this review we present in detail prototype CMS HLT physics selection algorithms, expected trigger rates and trigger performance in terms of both physics efficiency and timing.