Search for Higgs bosons in ${\rm e^+e^-}$ collisions at 183 GeV

Abstract.

The data collected by the OPAL experiment at $\sqrt s=183$ 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, $m_{\rm h^0} > 70.5$ GeV and $m_{\rm A^0} > 72.0$ GeV are obtained for $\tan{\beta}>1$, no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range $0.8 < \tan\beta < 1.9$ is excluded for minimal scalar top mixing and $m_{\mathrm{top}} \le 175$ GeV. More general scans of the MSSM parameter space are also considered.