Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions

TL;DR

This paper evaluates the performance of ATLAS muon chambers under LHC-like conditions, demonstrating high efficiency and minimal resolution degradation in high-background environments.

Contribution

It provides experimental results on the spatial resolution and efficiency of ATLAS muon drift chambers under simulated LHC background conditions.

Findings

Spatial resolution degrades by 4 microns at high background rates

Detection efficiency remains unchanged under irradiation

Tracking efficiency of 98% at maximum background rates

Abstract

For the muon spectrometer of the ATLAS detector at the large hadron collider (LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift tubes are used for precision tracking covering an active area of 5000 m2 in the toroidal field of superconducting air core magnets. The chambers have to provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an absolute pressure of 3 bar and gas gain of 2?104. The environment in which the chambers will be operated is characterized by high neutron and background with counting rates of up to 100 per square cm and second. The resolution and efficiency of a chamber from the serial production for ATLAS has been investigated in a 100 GeV muon beam at photon irradiation rates as expected during LHC operation. A silicon strip detector telescope was used as external reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m at the highest background rate. The detection efficiency of the drift tubes is unchanged under irradiation. A tracking efficiency of 98% at the highest rates has been demonstrated.