The polarization of the W boson in t --> Wb decay is unambiguously
predicted by the Standard Model of electroweak interactions and is a
powerful test of our understanding of the tbW vertex. We measure this
polarization from the invariant mass of the b quark from t --> Wb and the
lepton from W --> l nu whose momenta measure the W decay angle and direction
of motion, respectively. In this paper we present a measurement of the
decay rate (f_V+A) of the W produced from the decay of the top quark in the
hypothesis of V+A structure of the tWb vertex. We find no evidence for the
non-standard V+A vertex and set a limit on f_V+A < 0.80 at 95% confidence
level. By combining this result with a complementary observable in the same
data, we assign a limit on f_V+A < 0.61 at 95% CL. This corresponds to a
constraint on the right-handed helicity component of the W polarization of
f_+ < 0.18 at 95% CL. This limit is the first significant direct constraint
on f_V+A in top decay.
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Updated: Thursday, 2005 February 10 12:33:06 CST automatically from input from Carol Picciolo