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Measurement of the W Boson Helicity in Top Quark Decay at DØ

We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of tt̄ events in the lepton+jets and dilepton decay modes. These data correspond to an integrated luminosity of 370 pb, collected by the DØ detector at the Fermilab Tevatron pp̄ Collider at √ s = 1.96 TeV. We reconstruct the kinematics of the tt̄ and decay products, which allows for the measurement of the leptonic decay angle θ∗ for each event. By comparing the cos θ∗ distribution from the data with those for the expected background and signal for various values of f+, we find f+ = 0.08 ± 0.08(stat) ± 0.05(syst). This measurement is consistent with the standard model prediction of f+ = 3.6 × 10.