Search for V+A Current in Top-Quark Decays in pp¯ Collisions at s=1.96TeV

We report an upper limit on the fraction of V+A current, f_V+A, in top-quark decays, using approximately 700pb^-1 of pp¯ collisions at s=1.96TeV acquired by the upgraded Collider Detector at Fermilab. For the decay t→Wb→ℓνb (where ℓ=e or μ), the invariant mass of the charged lepton and the bottom quark jet is sensitive to the polarization of the W boson. We determine f_V+A=-0.06±0.25 given a top-quark mass of 175GeV/c². We set an upper limit on f_V+A of 0.29 at the 95% confidence level, an improvement by a factor of 2 on the previous best direct limit.