We present a search for a massive quark (t) decaying to Wq and thus mimicking the top quark decay signature in data collected by the CDF II detector corresponding to 2.8 fb^-1. We use the reconstructed mass of the t quark and the scalar sum of the transverse energies in the event to discriminate possible new physics from Standard Model processes, and set limits on a standard 4th generation t quark.
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