CMS Tracker Commissioning using cosmic muon data

Many physics channels, and in particular events containing top quarks, produce b jets in the final state which need to be distinguished from more copious backgrounds containing only light flavored jets. Tagging of b-jets, mainly relies upon relatively distinct properties of b-hadrons such as large proper lifetime, large mass, decays to final states with high charged track multiplicities. Precise spatial reconstruction close to the interaction point and efficient track reconstruction are key ingredients for all b-tagging algorithms. These rely on stable, low noise, low occupancy and highly efficient tracking detectors. This is a short review of the results of the studies on the CMS tracker performances carried out with cosmics at the CERN Tracker Integration Facility from march to july 2007, in order to show how this performance is in line with the requirement of the CMS community for a good b-tagging.