Bringing the ATLAS Muon Spectrometer to life with cosmic rays

The Muon Spectrometer of the ATLAS experiment at the Large Hadron Collider is the largest device ever built to track high energy particles. It has been designed to provide muon identification and measurement in the hard environment of proton–proton collisions at high energy and high luminosity at the LHC. An impressive number of elements, spread over the large volume of the spectrometer, were commissioned for many months with cosmic rays and were ready to take data when the first beam was circulated in the LHC. A systematic study of the detectorʹs performance was done in the following months. More than 200 million cosmic ray triggers were taken in different conditions. We present the status of the muon detectors and the main results from the reconstruction of this event sample, showing that the ATLAS Muon Spectrometer is well advanced towards physics data taking.