Abstract: We present a measurement of the top-quark width in the lepton þ jets decay channel of tt events produced in pp collisions at Fermilabs Tevatron collider and collected by the CDF II detector. From a data sample corresponding to 4:3 fb 1 of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of the hadronically decaying W boson that comes from the top-quark decay are reconstructed for each event and compared with templates of different top-quark widths (t) and deviations from nominal jet energy scale (JES) to perform a simultaneous fit for both parameters, where JES is used for the in situ calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95% confidence level (CL) of t < 7:6 GeV and a two-sided 68% CL interval of 0:3 GeV < t < 4:4 GeV for a top-quark mass of 172:5 GeV=c2, which are consistent with the standard model prediction

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