The first-level and high-level muon triggers of the Compact Muon Solenoid experiment at CERN

H Sakulin

doi:10.1109/nssmic.2003.1352048

Abstract

High transverse momentum muons are expected to play a crucial role in the discovery of the Standard Model Higgs, precision Standard Model measurements, as well as in the discovery of new physics such as Supersymmetry at CERN's new Large Hadron Collider. In order to provide efficient and precise muon detection, three muon systems are utilized in the Compact Muon Solenoid (CMS) experiment: Drift Tubes in the barrel, Cathode Strip Chambers in the endcaps and Resistive Plate Chambers throughout for trigger information complementary to the high-precision tracking measurements of the first two systems. The CMS trigger has to reduce the event rate from the LHC bunch-crossing rate of 40 MHz to a rate of approximately 100 Hz, the maximum that can be recorded for offline analysis. This enormous reduction is achieved in several subsequent levels: while the first level trigger reduces the initial rate to a maximum of 100 kHz employing fully pipelined custom-built electronics, the following higher trigger levels will run on a high-performance farm of commercial processors allowing for full flexibility. Muon-trigger algorithms employed at the first and higher trigger levels are discussed. Special emphasis is given to the First-Level Global Muon Trigger, which increases efficiency and considerably improves rate reduction by optimally combining trigger information of all three muon systems. Detailed Monte-Carlo simulations of expected trigger rates and trigger efficiencies are presented.

Highlights

CERN’s new Large Hadron Collider (LHC) will provide proton-proton collisions with a center-of-mass energy of 14 TeV, roughly 7 times that of the current most powerful machine, the Tevatron II
Abstract--High transverse momentum muons are expected to play a crucial role in the discovery of the Standard Model Higgs, precision Standard Model measurements, as well as in the discovery of new physics such as Supersymmetry at CERN’s new Large Hadron Collider
In order to provide efficient and precise muon detection, three muon systems are utilized in the Compact Muon Solenoid (CMS) experiment: Drift Tubes in the barrel, Cathode Strip Chambers in the endcaps and Resistive Plate Chambers throughout for trigger information complementary to the high-precision tracking measurements of the first two systems

Summary

INTRODUCTION

CERN’s new Large Hadron Collider (LHC) will provide proton-proton collisions with a center-of-mass energy of 14 TeV, roughly 7 times that of the current most powerful machine, the Tevatron II. CMS has chosen to perform this rate reduction employing only two physical layers as illustrated in Fig. 1: the first step of reduction is performed by the Level-1 Trigger [3], a large system of fully pipelined custom-built electronics which processes data from every bunch crossing without dead-time. Based on coarsely segmented data from the calorimeters and muon system, the Level-1 Trigger reduces the rate below 100 kHz while the full high-precision data are kept in frontend pipelines. Reconstruction proceeds in virtual trigger levels: virtual "Level-2" algorithms select events using fast algorithms based on the muon system and calorimeters. After this step tracker data are included in order to perform a finer selection. All three muon systems are used both in the First-Level and the High-Level Muon Trigger

FIRST LEVEL TRIGGER

HIGH-LEVEL TRIGGER

SIMULATED PERFORMANCE

SUMMARY