Search for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>V</mml:mi><mml:mo>+</mml:mo><mml:mi>A</mml:mi></mml:math>Current in Top-Quark Decays in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi><mml:mover accent="true"><mml:mi>p</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math>Collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>1.96</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:math>

We report an upper limit on the fraction of $V+A$ current, ${f}_{V+A}$, in top-quark decays, using approximately $700\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ acquired by the upgraded Collider Detector at Fermilab. For the decay $t\ensuremath{\rightarrow}Wb\ensuremath{\rightarrow}\ensuremath{\ell}\ensuremath{\nu}b$ (where $\ensuremath{\ell}=e$ or $\ensuremath{\mu}$), the invariant mass of the charged lepton and the bottom quark jet is sensitive to the polarization of the $W$ boson. We determine ${f}_{V+A}=\ensuremath{-}0.06\ifmmode\pm\else\textpm\fi{}0.25$ given a top-quark mass of $175\text{ }\text{ }\mathrm{GeV}/{c}^{2}$. 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.

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