Performance of Michigan sMDT Prototype Chambers for the HL-LHC ATLAS Muon Detector Upgrade

TL;DR

This paper evaluates the performance of new small-diameter Monitored Drift Tube (sMDT) chambers designed for the ATLAS muon spectrometer upgrade at HL-LHC, demonstrating high resolution and efficiency improvements with advanced electronics.

Contribution

It presents the first measurements of tracking resolution and efficiency of prototype sMDT chambers for HL-LHC, including the impact of new high-gain readout electronics.

Findings

Tracking resolution around 102 μm with standard electronics.

Improved resolution to 83.4 μm with new electronics.

Average hit efficiency of 98.5%.

Abstract

A new small-diameter Monitored Drift Tube (sMDT) chamber has been developed for the muon spectrometer of the ATLAS experiment to handle the higher collision rates expected at the CERN High Luminosity Large Hadron Collider (HL-LHC). This paper presents measurements of the tracking resolution and hit efficiency of two prototype sMDT chambers constructed at the University of Michigan. Using cosmic-ray muons the sMDT tracking resolution of 103.7$\pm8.1$ \textmu m was measured for one chamber and 101.8$\pm$7.8 \textmu m for the other, compared with a design resolution of 106 \textmu m. A further tracking resolution improvement to 83.4$\pm$7.8 \textmu m was obtained by using new high-gain readout electronics which will be added for HL-LHC. An average tracking efficiency of (98.5$\pm$0.2)\% was found for both chambers. The methodology used to determine the detector tracking resolution and efficiency, including reconstruction of sMDT data and a Geant4 simulation of the test chamber, is presented in detail.