Higgs boson searches at LEP I and LEP II

The different topological searches that were carried out at LEP I to search for the Higgs boson(s) predicted in the standard model or in its minimal supersymmetric extension (MSSM) have been outlined. A few candidates events were found by each of the four LEP experiments in several topologies, all consistent with the background expectation from the standard model of electroweak interactions. A combination of these unsuccessful analyses allows a 95% C.L. lower limit of 65.2 GeV/c2 to be set on the standard model Higgs boson mass, and to exclude the existence of the lighter CP-even (h) and the CP-odd (A) neutral Higgs bosons of the MSSM with masses below 45.5 GeV/c2. A summary of the LEP II capabilities in these respects has also been presented. A lower limit could be set for the standard model Higgs boson up to approximately √s - mZ - 2 GeV/c2, provided that excellent b-tagging efficiencies are achieved. The whole MSSM parameter space (mA, tanβ) could even be totally explored, for moderate top mass and stop mixing parameters, if the centre-of-mass energy reached 205 GeV. (author)