We use the transverse momentum spectrum of leptons in the decay
chain t --> bW with W --> l nu to measure the helicity of the W bosons in the
top quark rest frame. Our measurement uses a tt-bar sample isolated in 106
+/- 4 pb-1 of data collected in p anti-p collisions at s**(1/2) = 1.8 TeV with the
CDF detector at the Fermilab Tevatron. Assuming a standard V-A weak decay, we
find that the fraction of W's with zero helicity in the top rest frame is F_0
= 0.91 +/- 0.37(stat) +/- 0.13(syst), consistent with the standard model
prediction of F+0 = 0.70 for a top mass of 175 GeV/c2.
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Updated: Thursday, 2000 January 06 08:45:11 CST automatically from input from CAROL@FNALD.FNAL.GOV