We present a measurement of the W-boson polarization in top-quark decays in t (t) over bar events with decays to dilepton final states using data corresponding to 5.1 fb(-1) of integrated luminosity in p (p) over bar collisions collected by the CDF II detector at the Tevatron. Assuming a top-quark mass of 172.5 GeV/c(2), a simultaneous measurement of the fractions of longitudinal (f(0)) and right-handed (f(+)) W-bosons yields the results f(0) = 0.70(-0.17)(+0.18)(stat) +/- 0.06(syst) and f(+) = -0.09 +/- 0.09(stat) +/- 0:03(syst). Combining this measurement with our previous measurement based on single-lepton final states, we obtain f(0) = 0.84 +/- 0.09(stat) +/- 0.05(syst) and f(+) = -0.16 +/- 0.05(stat) +/- 0.04(syst). The results are consistent with the standard model expectation. (C) 2013 Elsevier B.V. All rights reserved.
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