Measurement of the W boson helicity in top quark decays at DO

Abstract

We present a measurement of the fraction f₊ of right-handed W bosons produced in top quark decays, based on a candidate sample of tt^- events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370pb^-1 collected by the D∅ detector at the Fermilab Tevatron pp^- Collider at √s=1.96TeV. We reconstruct the decay angle θ^∗ for each lepton. By comparing the cosθ^∗ distribution from the data with that for the expected background and signal for various values of f₊ (where we assume that the fraction of longitudinally-polarized W bosons has the standard model value of 0.70), we find f₊=0.056±0.080(stat)±0.057(syst) (f₊Ũ0.23 at 95% C.L.), consistent with the standard model prediction of f₊=3.6x10^-4.