Search for Higgs bosons in

Abstract

The data collected by the OPAL experiment at √ s = 183 GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated luminosity of approximately 54 pb −1 . None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background. This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, m h 0 > 70.5 GeV and m A 0 > 72.0 GeV are obtained for tan β > 1, no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range 0.8 < tan β < 1.9 is excluded for minimal scalar top mixing and m top ≤ 175 GeV. More general scans of the MSSM parameter space are also considered.

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

“…The analysis closely follows our published one at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sqrt{s}=183\ \mbox{GeV}$\end{document} [16]. It proceeds in two steps.…”

“…For each individual mass region, at each center-of-mass energy, we create a separate likelihood selection. The definition of the likelihood function is based on a set of histograms of channel specific observables, given in [16]. The signal histograms are built using events generated at m ref .…”

“…The event selection follows our published analysis at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sqrt{s}=183\ \mbox{GeV}$\end{document} [16]: first, well-separated four-jet events with large visible energy are preselected; then a set of variables is combined using a likelihood technique. To improve the discriminating power of the likelihood selection, a new reference variable is introduced: the logarithm of the matrix element probability for W + W − production averaged over all possible jet-parton assignments computed by EXCALIBUR [40].…”

“…1(e)–(h). The Higgs-boson mass can be reconstructed with a resolution of 1–1.5 GeV [16]. Figure 2(b) shows the mass dependence of the expected number of background and signal events and compares them to the observed number of events at each test mass.…”

“…The previously published OPAL lower limit on the charged Higgs-boson mass, under the assumption of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mbox {$\mathrm {BR}(\mbox {$\mathrm {H}^{\pm }$}\mbox {$\rightarrow $}\mbox {${\tau \nu _{\tau }}$})$}+ \mbox {$\mathrm {BR}(\mbox {$\mathrm {H}^{\pm }$}\mbox {$\rightarrow $}\mbox {$\mathrm {q}\bar {\mathrm {q}}$})$}= 1$\end{document}, is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$m_{\mathrm{H}^{\pm}}>59.5\ \mbox{GeV}$\end{document} at 95 % confidence level (CL) using data collected at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sqrt{s}\leq183\ \mbox{GeV}$\end{document} [15, 16]. Lower bounds of 74.4–79.3 GeV have been reported by the other LEP collaborations [17–19] based on the full LEP2 data set.…”