Development of fast high-resolution muon drift-tube detectors for high counting rates

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 628; no. 1; pp. 154 - 157
• Main Authors: Bittner, B., Dubbert, J., Horvat, S., Kortner, O., Kroha, H., Legger, F., Richter, R., Adomeit, S., Biebel, O., Engl, A., Hertenberger, R., Rauscher, F., Zibell, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2011
• Subjects: Chambers; Counting; Detectors; Drift; Drift tubes; High rates; LHC; Muon chambers; Muons; Spectrometers; Drift tubes; High rates; LHC; Muon chambers
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2010.06.306

Pressurized drift-tube chambers are efficient detectors for high-precision tracking over large areas. The Monitored Drift-Tube (MDT) chambers of the muon spectrometer of the ATLAS detector at the Large Hadron Collider (LHC) reach a spatial resolution of 35 μ m and almost 100% tracking efficiency with 6 layers of 30 mm diameter drift tubes operated with an Ar:CO 2 (93:7) gas mixture at 3 bar and a gas gain of 20 000. The ATLAS MDT chambers are designed to cope with background counting rates due to neutrons and γ rays of up to about 300 kHz per tube which will be exceeded for LHC luminosities larger than the design value of 10 34 cm −1 s −1. Decreasing the drift-tube diameter to 15 mm while keeping the other parameters, including the gas gain, unchanged reduces the maximum drift time from about 700 to 200 ns and the drift-tube occupancy by a factor of 7. New drift-tube chambers for the endcap regions of the ATLAS muon spectrometer have been designed. A prototype chamber consisting of 12 times 8 layers of 15 mm diameter drift tubes of 1 m length has been constructed with a sense wire positioning accuracy of 20 μ m . The 15 mm diameter drift-tubes have been tested with cosmic rays in the Gamma Irradiation Facility at CERN at γ counting rates of up to 1.85 MHz.