Expectations for observation of top-quark pair production in the dileptonic final state in early CMS data at sqrt s = 10TeV

The dileptonic decay channel of the top-quark pair production at LHC is the best candidate for an early observation of a process involving top-quark. Due to its clean signature (two isolated and high Pt leptons with opposite charge, two b-jets and missing transverse energy) and its large cross-section, the expected background events can be sufficiently reduced to allow a rediscovery after few inverse picobarns of integrated luminosity. This presentation describes the result of the study done at $\sqrt s=$10~TeV for 10 pb$^{-1}$ of integrated luminosity, for electrons and muons in the final states. It presents the expected precision of the cross-section measurement and covers the description of the simulation and the backgrounds, the event selection, the data-driven background estimation methods, the systematics uncertainties evaluation and two alternative studies (tracker-based study and b-quark content study).