Combination of CDF and D0 Measurements of the W boson Helicity in Top Quark Decays
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We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of the 2.7-5.4 fb-1 of pp- collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of the W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0= 0.722 ± 0.081[±0.062(stat) ± 0.052(syst)] and f+ = -0.033 ± 0.046[±0.034(stat) ± 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 ± 0.057[±0.035(stat) ± 0.046(syst)] for fixed f+ and f+ = -0.015 ± 0.035[±0.018(stat) ± 0.030(syst)] for fixed f0. The results are consistent with standard model expectations.