The Muon Spectrometer Barrel Level-1 Trigger of the ATLAS Experiment at LHC

A Aloisio,R Vari,G Ciapetti,R De Asmundis,L Luminari,S Veneziano,V Izzo,A Migliaccio,C Luci,A Salamon,A Di Mattia,G Carlino,F Pastore,E Petrolo,A Nisati,F Conventi

doi:10.1109/tns.2006.877044

Abstract

The proton-proton beam crossing at the LHC accelerator at CERN will have a rate of 40 MHz at the project luminosity. The ATLAS Trigger System has been designed in three levels in order to select only interesting physics events reducing from that rate of 40 MHz to the foreseen storage rate of about 200 Hz. The First Level reduces the output rate to about 100 kHz. The ATLAS Muon Spectrometer has been designed to perform stand-alone triggering and measurement of Muon transverse momentum up to 1 TeV/c with good resolution (from 3% at 10 GeV/c up to 10% at 1 TeV/c). In the Barrel region of the Muon Spectrometer the Level-1 trigger is given by means of three layers of resistive plate chamber detectors (RPC): a gaseous detector working in avalanche mode composed by two plates of high-resistivity bakelite and two orthogonal planes of read-out strips. The logic of the Level-1 barrel Muon trigger is based on the search of patterns of RPC hits in the three layers consistent with a high transverse momentum Muon track originated from the interaction vertex. The associated trigger electronics is based on dedicated processors, the Coincidence Matrix boards, performing space coincidences and time gates and providing the RPC readout as well. A detailed simulation of the ATLAS Experiment and of both the hardware components and the logic of the Level-1 Muon Trigger in the barrel of the Muon Spectrometer has been performed. This simulation has been used not only to evaluate the performances of the system but also to define the hardware set-up such as the cabling of both the trigger detectors and the trigger electronics modules. A description of both the Level-1 Muon Trigger system in the barrel and the RPC detectors, with their cosmic rays quality tests, will be presented together with the trigger performances and rates calculations evaluated for Muons over a wide range of pT and preliminary studies on the impact of accidental triggers due to low energy background particles in the experimental area

Highlights

The proton-proton Collider LHC at CERN, currently under construction, has a design luminosity of L =1034 cm-2s-1 with a centre of mass energy of 14 TeV and a bunch crossing rate of 40 MHz
The logic of the Level-1 barrel muon trigger is based on the search of patterns of Resistive Plate Chamber detectors (RPC) hits in the three layers consistent with a high transverse momentum muon track originated from the interaction vertex
RPC detector are used in ATLAS as trigger detectors for the barrel muon spectrometer

Summary

Introduction

The proton-proton Collider LHC at CERN, currently under construction, has a design luminosity of L =1034 cm-2s-1 with a centre of mass energy of 14 TeV and a bunch crossing rate of 40 MHz. The logic of the Level-1 barrel muon trigger is based on the search of patterns of RPC hits in the three layers consistent with a high transverse momentum muon track originated from the interaction vertex.

Results

Conclusion