Combination of CDF and D0 measurements of the W boson helicity in top quark decays
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 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 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.