Exclusion of an exotic top quark with -4/3 electric charge using soft lepton tagging

We present a measurement of the electric charge of the top quark using pp̄ collisions corresponding to an integrated luminosity of 2.7fb -1 at the CDF II detector. We reconstruct tt̄ events in the lepton+jets final state. We use soft lepton taggers to determine the flavor of the b jets, which we use to reconstruct the top quark's electric charge and exclude an exotic top quark with -4/3 charge at 95% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose. © 2010 The American Physical Society.