Flavour-independent h⁰A⁰ search and two Higgs doublet model interpretation of neutral Higgs boson searches at LEP

Abstract.

Upper limits on the cross-section of the pair-production process ${\ensuremath{{\mathrm{e}}^ + {\mathrm{e}}^-}} \to \mathrm{h}^0 \mathrm{A}^0$, assuming 100 $\%$ branching fraction to hadrons, are derived from a new search for the $\mathrm{h}^0\mathrm{A}^0 \to$ hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h⁰ and A⁰, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the $\mathrm{h}^0, \mathrm{A}^0 \to \mathrm{q\bar{q}}, {\ensuremath{\mathrm{g}\mathrm{g}}}, {\ensuremath{\tau^ + \tau^-}}$ and $\mathrm{h}^0\to\mathrm{A}^0\mathrm{A}^0$ decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the ($m_{\mathrm{h}}, m_{\mathrm{A}}), (m_{\mathrm{h}}, \tan{\beta})$ and $(m_{\mathrm{A}}, \tan{\beta})$ planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region $1 \lesssim m_{\mathrm{h}} \lesssim 55$ GeV and $3 \lesssim m_{\mathrm{A}} \lesssim 63$ GeV is excluded at 95 % CL, independently of $m_{\mathrm{h}}, m_{\mathrm{A}}, \tan{\beta}$ and for selected values of $\alpha$ which are representative of a complete $\alpha$-scan.