The trigger chambers of the ATLAS muon spectrometer: Production and tests

The ATLAS Muon Spectrometer (ATLAS Collaboration, ATLAS Muon Spectrometer Technical Design Report CERN/LHCC/97-22, ATLAS TDR 10, 1997.) will use dedicated detectors to trigger on muons and to identify the bunch-crossing at the appropriate rate. The Spectrometer has been designed to perform stand-alone triggering and measurement of muon transverse momentum up to 1 TeV with good resolution (from 3% up to 10% at 1 TeV). The magnetic system is composed of three large superconducting air-core toroids instrumented with trigger and highprecision tracking chambers, a central part (barrel) composed of eight coils and two end-cap magnets. The high-precision tracking system is based on Monitored Drift Tube (MDT) and Cathode Strip Chambers (CSC) in the small angle-regions. The Level-1 trigger is provided by Resistive Plate Chambers (RFC) in the barrel and Thin Gap Chambers (TGC) in the end-cap. These detectors will also measure the track coordinates in the magnetic field direction (second coordinate), to complement the precision tracking provided by the MDT which only measure the track coordinates in the bending direction of the magnetic field. The trigger system covers an area of 3650 m² in the barrel and 2900m² in the end-cap. In the barrel region three double-gap RPC stations are used, two in the middle and one in the outer MDT chamber layer. In the end-cap region one triple-gap TGC station is used, in front of the middle MDT station, and two double-gap TGC stations behind it. The mass production of both systems is under way. The systems were involved in extensive beam tests in 2002-2003, testing their compliance with LHC timing requirements using 25 ns beam bunching to emulate the LHC beam structure, aging under critical environment conditions and so on.