Extensive performance studies for the ATLAS BIS-MDT precision muon chambers with cosmic rays

ATLAS (A Toroidal LHC ApparatuS) is a general-purpose experiment, which will start its operation at the Large Hadron Collider (LHC) at CERN in 2007. The ATLAS detector is designed to explore numerous physics processes by measuring, recording, and investigating the products emerging from proton-proton collisions at energies up to 14 TeV. High-precision muon momentum measurement (dp/p-10% at p_T=1 TeV/c) over large areas using Monitored Drift Tube (MDT) chambers is crucial for the ATLAS experiment. More than 1,200 MDT chambers, assembled from approximately 370,000 drift tubes operated at 3 bar pressure, will be used to provide for the total detector coverage of 5,500 m². Three Greek universities have taken the responsibility to construct 30,000 drift tubes of ∼1.7 in length, to test them and finally assemble them into 120 BIS (Barrel Inner Small) chambers. The design of the muon drift tubes aims at high efficiency (>95%) and a spatial resolution of <80 μm (single tube resolution). This paper describes the cosmic ray setup, which has been instrumented in order to verify. that the BIS chamber Module-0 fulfils its design requirements. The analysis of its data shows that the chamber meets these requirements; it has low noise levels, uniform drift properties, good spatial resolution and high particle detection efficiency.