Data quality monitor of the muon spectrometer tracking detectors of the ATLAS experiment at the Large Hadron Collider: First experience with cosmic rays

The Muon Spectrometer of the ATLAS experiment at the CERN Large Hadron Collider is completely installed and many data have been collected with cosmic rays in different trigger configurations. In the barrel part of the spectrometer, cosmic ray muons are triggered with Resistive Plate Chambers, RPC, and tracks are obtained joining segments reconstructed in three measurement stations equipped with arrays of high-pressure drift tubes, MDT. The data are used to validate the software tools for the data extraction, to assess the quality of the drift tubes response and to test the performance of the tracking programs. We present a first survey of the MDT data quality based on large samples of cosmic ray data selected by the second level processors for the calibration stream. This data stream was set up to provide high statistics needed for the continuous monitor and calibration of the drift tubes response. Track segments in each measurement station are used to define quality criteria and to assess the overall performance of the MDT detectors. Though these data were taken in not optimized conditions, when the gas temperature and pressure was not stabilized, the analysis of track segments shows that the MDT detector system works properly and indicates that the efficiency and space resolution are in line with the results obtained with previous tests with a high energy muon beam.