We present the measurements of the fraction of
longitudinally (f0) and right-handed
(f+) polarized W bosons from top quark
decay using tt events with the dilepton final
W boson helicity fractions are determined by a comparison of angular
distribution of leptons in W rest-frame (cos θ*) with
the templates corresponding to left-handed, right-handed an
longitudinal fractions exclusively.
Using CDF Run II data corresponding to integrated
luminosity of 4.8 fb-1, three measurements are performed.
A model independent simultaneous measurement of
f0 and f+ yields
f0 = 0.78 +0.19-0.20 (stat.) +- 0.06 (syst.)
A measurement of f0 constraining
f+ to its Standard Model
value of 0.0 yields
f+ = -0.12 +0.11-0.10 (stat.) +- 0.04 (syst.)
f0 = 0.62 +- 0.11 (stat.) +- 0.06 (syst.)
while a measurement of f+ constraining
f0 to its Standard Model value of 0.70 gives
f+ = -0.07 + 0.06- 0.05 (stat.) +- 0.03 (syst.)
All the results are consistent with Standard Model expectations.