Search for charged Higgs bosons in e+e− collisions at \sqrt{s}=189\mbox{--}209\ \mbox{GeV}

A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at \(\sqrt{s}=189\mbox{--}209\ \mbox{GeV}\), corresponding to an integrated luminosity of approximately 600 pb−1. Charged Higgs bosons are assumed to be pair-produced and to decay into \(\mathrm{q} \bar{\mathrm{q}}\), τντ or AW±. No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption \(\mathrm{BR} (\mathrm{H}^{\pm} \to \tau\nu_{\tau}) + \mathrm{BR} (\mathrm{H}^{\pm} \to \mathrm{q} \bar{\mathrm{q}}) = 1\), motivated by general 2HDM type II models, excluded areas on the \([m_{\mathrm{H}^{\pm}} , \mathrm{BR} (\mathrm {H}^{\pm} \to \tau\nu_{\tau})]\) plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H±→τντ). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses \(m_{\mathrm{H}^{\pm}}\) and mA are presented for different choices of tanβ.