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

Abstract

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 $2.7-5.4\text{ fb}^{-1}$ of $p\bar{p}$ collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of $W$ bosons with longitudinal $(f_ 0)$ and right-handed $(f_ +)$ helicities, we find $f_ 0 =0.722±0.081[±0.062(\text{stat})±0.052(\text{syst})]$ and $f_+ =-0.033±0.046[±0.034(\text{stat})±0.031(\text{syst})]$. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find $f_0 =0.682±0.057[±0.035(\text{stat})±0.046(\text{syst})]$ for fixed $f_ +$ and $f_ + =-0.015±0.035[±0.018(\text{stat})±0.030(\text{syst})]$ for fixed $f_ 0$. The results are consistent with standard model expectations.