Search for Charged Higgs Bosons in Decays of Top Quarks in p anti-p Collisions at s**(1/2) =1.96 TeV

We report on the first direct search for charged Higgs boson decaying into cs-bar in tt-bar events produced by p anti-p collisions at s**(1/2) = 1.96 TeV. The search uses a data sample corresponding to an integrated luminosity of 2.2 fb-1 collected by the CDF II detector at Fermilab and looks for a resonance in the invariant mass distribution of two jets in the lepton+jets sample of tt-bar candidates. We observe no evidence of charged Higgs bosons in top quark decays. Hence, 95% upper limits on the top quark decay branching ratio are placed at B(t --> H+b) < 0.1 to 0.3 for charged Higgs boson masses of 60 to 150 GeV/c2 assuming B(H+ --> cs-bar) =1.0. The upper limits on B(t --> H+b) are also used as model-independent limits on the decay branching ratio of top quarks to generic scalar charged bosons beyond the standard model.