Two Higgs Doublet Model and model independent interpretation of neutral Higgs boson searches

Searches for the neutral Higgs bosons \(\mathrm{h}^0\) and \(\mathrm{A}^0\) are used to obtain limits on the Type II Two Higgs Doublet Model (2HDM(II)) with no CP–violation in the Higgs sector and no additional particles besides the five Higgs bosons. The analysis combines approximately 170 pb\(^{-1}\) of data collected with the OPAL detector at \(\sqrt{s} \approx 189\) GeV with previous runs at \(\sqrt{s} \approx m_Z\) and \(\sqrt{s} \approx 183\) GeV. The searches are sensitive to the \(\mathrm{h}^0, \mathrm{A}^0\rightarrow\mathrm{q}\bar{\mathrm{q}}, \mathrm{g}\mathrm{g}, \tau^+\tau^-\) and \(\mathrm{h}^0\rightarrow\mathrm{A}^0\mathrm{A}^0\) decay modes of the Higgs bosons. For the first time, the 2HDM(II) parameter space is explored in a detailed scan, and new flavour independent analyses are applied to examine regions in which the neutral Higgs bosons decay predominantly into light quarks or gluons. Model–independent limits are also given.