Search for V+A current in top-quark decays in pp̄ collisions at s=1.96TeV

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