Test of CMS Muon Barrel Drift Chambers with Cosmic Rays

Production of the muon barrel drift chambers called MB3 for the CMS experiment at the LHC has started at Legnaro INFN Labs in 2001. Detectors are fully equipped with the final front-end and high-voltage boards, and test pulse and low-voltage systems. Before being moved to CERN, all chambers are tested and validated. After good noise level and proper high voltage behavior have been ensured, we collect cosmic-ray events triggered by an external scintillator system. We use those data to infer about the main parameters of the chambers, namely, detection efficiency, uniformity in the behavior, timing properties (resolution, uniformity, dependence on the track angle), and possible shifts of the wires and of the layers inside the superlayers. The method is particularly efficient in finding pathologies caused by trivial mistakes like, for example, an unconnected electrode, which can be quickly recovered.