Search for Charged Higgs Bosons in Decays of Top Quarks inpp¯Collisions ats=1.96TeV

We report on the first direct search for charged Higgs bosons decaying into $c\overline{s}$ in $t\overline{t}$ events produced by $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The search uses a data sample corresponding to an integrated luminosity of $2.2{\mathrm{fb}}^{-1}$ collected by the CDF II detector at Fermilab and looks for a resonance in the invariant mass distribution of two jets in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ sample of $t\overline{t}$ 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 $\mathcal{B}(t\to H^{+}b)<$ 0.1 to 0.3 for charged Higgs boson masses of 60 to $150\mathrm{GeV}/c^2$ assuming $\mathcal{B}(H^{+}\to c\overline{s})=1.0$. The upper limits on $\mathcal{B}(t\to H^{+}b)$ are also used as model-independent limits on the decay branching ratio of top quarks to generic scalar charged bosons beyond the standard model.