We present a measurement of the electric charge of the top
quark using p anti-p collisions corresponding to an integrated luminosity
of 2.7 fb-1 at the CDF II detector. We reconstruct tt-bar events in
the lepton + jets final state and use kinematic information to determine
which b-jet is associated with the leptonically- or hadronically-decaying
t-quark. Soft lepton taggers are used to determine the b-jet flavor.
Along with the charge of the W boson decay lepton, this information
permits the reconstruction of the top quark's electric charge. Out of
45 reconstructed events with 2.4 +/- 0.8 expected background events,
29 are reconstructed as tt-bar with the standard model +2/3 charge,
whereas 16 are reconstructed as tt-bar with an exotic -4/3 charge.
This is consistent with the standard model and excludes the exotic
scenario at 95% confidence level. This is the strongest exclusion of the
exotic charge scenario and the first to use soft leptons for this purpose.
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Updated: Thursday, 2010 September 23 15:45:23 CDT automatically from input from Carol Picciolo