Speaker
Summary
In the framework of the standard model (SM), the Top quark is expected to decay to a W-boson and a b-quark 99.8% of the times due to the Cabibbo-Kobayashi-Maskawa (CKM) matrix element Vtb being close to unity. The current experimental limits from Tevatron on the measurement of Vtb from top pairs ttbar and single top production are consistent with the SM predictions. Higher energy of proton-proton collisions and larger top quark production cross section at the Large Hadron Collider (LHC) may provide an improved reach in the measurement of Vtb. We present two analyses dedicated to measure the ratio of branching ratios of the top quark using ttbar events with either one or two prompt isolated leptons (e or mu) in the final state. The sensitivity of the measurement with the CMS experiment is evaluated after particle identification and detector reconstruction. Data-driven techniques to control the background in the selected events are discussed and the expected simulation results are presented for the first physics run of LHC. We also discuss how the method can be used to measure directly from data the efficiency of the algorithms used to discriminate jets coming from the hadronization of b quarks from the lighter quarks and gluons (b-tagging).
