First cosmic ray results of the ATLAS barrel muon spectrometer with magnetic field

The ATLAS experiment at the large hadron collider (LHC) at CERN is currently being assembled to be ready to take first data in 2008. Its muon spectrometer is designed to achieve a momentum resolution of better than 10% up to transverse muon momenta of 1 TeV. The spectrometer consists of one barrel and two endcap superconducting air-core toroid magnets instrumented with three layers of precision drift chambers as tracking detectors and a dedicated trigger system. First results of the cosmic ray test of the barrel muon spectrometer with magnetic field are presented, including results of the calibration of the drift chambers and of the spectrometer alignment.