W-boson polarization measurement in the t t ¯ dilepton channel using the CDF II detector

© 2013 Elsevier B.V. All rights reserved. We present a measurement of the W-boson polarization in top-quark decays in tt- events with decays to dilepton final states using data corresponding to 5.1 fb-1 of integrated luminosity in pp- collisions collected by the CDF II detector at the Tevatron. Assuming a top-quark mass of 172.5 GeV/c2, a simultaneous measurement of the fractions of longitudinal ( f0) and right-handed ( f+) W-bosons yields the results f0 = 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 f0 = 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.