Search for Yukawa production of a light neutral Higgs boson at LEP

Abstract

Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4-12 GeV has been performed in the Yukawa process e +e- → bb̄A/h → bb̄τ +τ-, using the data collected by the OPAL detector at LEP between 1992 and 1995 in e+e- collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on ζdA = | tan β| and ζdh = |sinα/cos β| for the production of the CP-odd A and the CP-even h, respectively, where tan β is the ratio of the vacuum expectat..