Probing the Heavy Flavor Content in t tbar Events and Using t tbar Events as a Calibration Tool at CMS

We present two analyses dedicated to measure the ratio of branching ratios of the top quark, R=B(t->Wb)/(t->Wq) (where q=d,s,b), using ttbar events with either one or two prompt isolated leptons (e or mu) in the final state. Furthermore the framework of the dileptonic analysis was used also for a feasibility study of the measurement of b-tagging efficiency, by assuming the R value to be the Standard Model one. Data-driven techniques to control the background in the selected events are discussed and the expected simulation results are presented.