Upgrades of the ATLAS muon spectrometer with new small-diameter drift tube chambers

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2019-08, Vol.936, p.509-510
• Main Authors: Kortner, O., Kroha, H., Nowak, S., Podkladkin, S., Rieck, P., Schmidt-Sommerfeld, K., Takasugi, E., Walbrecht, V., Fakhrutdinov, R., Kozhin, A.
• Format: Article
• Language: English
• Subjects: ATLAS detector; Drift-tube detectors; MDT chambers; Muon precision tracking; sMDT chambers
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2018.11.059

Small diameter muon drift-tube (sMDT) chambers with 15 mm tube diameter provide excellent spatial resolution like the MDT chambers with 30 mm tube diameter used in the ATLAS muon spectrometer so far, but can be operated at ten times higher background rates and allow for the instrumentation of regions where MDT chambers do not fit in. In April 2014 two such chambers (called BME) have been installed at the bottom of the barrel middle layer of the muon spectrometer, followed in January 2016 by another 12 sMDT chambers (called BMG) inserted in the detector feet in the barrel middle layer. They are since then operational in ATLAS, increasing the acceptance for precision muon momentum measurement in all three chamber layers. An unprecedently high sense wire positioning accuracy of 5μm (rms) has been achieved. In the next long LHC shutdown 2019–2020, 16 new sMDT chambers (called BIS 78) will be installed in the barrel inner layer in the transition region to the endcaps in order to make room for the installation of new RPC muon trigger chambers which will reduce the accidental trigger rate in this region as required for operation at the high-luminosity upgrade of the LHC (HL-LHC). This is a pilot project for the complete replacement of the MDT chambers in the small azimuthal sectors of the barrel inner layer (called BIS 1-6) by integrated sMDT-RPC detectors in the long shutdown 2024–2026 for the upgrade to HL-LHC. •Small-diameter muon drift tube (sMDT) chambers used for ATLAS muon system upgrades.•sMDTs with 1/2 the tube diameter have 10 x higher rate capability than the present ATLAS MDT chambers.•A record sense wire positioning accuracy of better than 5 μm has been achieved for sMDT chambers.•14 sMDT chambers are in operation, 16 more under construction for installation in 2019/20.•96 sMDT chambers will replace the MDT chambers in the barrel muon detector inner layer for HL-LHC.