We present a measurement of the top-quark width using tt-bar
events produced in p anti-p collisions at Fermilab's Tevatron collider
and collected by the CDF II detector. In the mode where the top quark
decays to a W boson and a bottom quark, we select events in which one W
decays leptonically and the other hadronically (lepton + jets channel).
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 W boson
that decays hadronically are reconstructed for each event and compared
with templates of different top-quark widths (Gamma's) and deviations
from nominal jet energy sale (Delta_JES) to perform a simultaneous fit
for both parameters, where Delta_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 Gamma_t <
7.6 GeV and a two-sided 68% CL interval of 0.3 GeV < Gamma_t <
4.4 GeV for a top-quark mass of 172.5 GeV/c2, which are consistent with
the standard model prediction. This is the first direct measurement of
Gamma_t to set a lower limit with 68% CL.
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Updated: Wednesday, 2010 December 22 13:55:05 CST automatically from input from Carol Picciolo