We explore the prospect of charged Higgs boson search in top quark decay at the Tevatron collider upgrade, taking advantage of the opposite states of $\tau$ polarization resulting from the $H^\pm$ and $W^\pm$ decays. Methods of distinguishing the two contr
reduction in the signal size in the?rst case,while there is no such price to pay
in the second.Consequently the latter strategy o?ers the best discovery limit
for the charged Higgs boson.We have explored these discovery limits in the
parameter space of H±mass and tanβassuming an integrated luminosity of
～2fb?1for the Tevatron upgrade.For the sake of completeness we have also explored the signal and discovery limit for the suggested Tevatron?and Dite-
vatron options,corresponding to an order of magnitude increase of luminosity
and a doubling of the CM energy respectively.
Acknowledgements