Higgs Boson Searches at LEP 2

In this talk preliminary results of Higgs boson searches at LEP2 up to centre-of-mass energies of 183 GeV have been summarised. The main topics are searches for the Minimal Standard Model (MSM) Higgs boson and searches for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM). No indication for Higgs production has been found. The experiments have published their Higgs search results for p s=133 GeV up to p s=172 GeV. A preliminary combination of these results yields a mass limit on the Standard Model Higgs boson of 77.5 GeV/c 2 at 95% CL. During the winter conferences 1998 rst results of the 1997 data taking at p s=183 GeV have been presented. Individual limits of the experiments on the MSM Higgs boson mass are around 85 GeV/c 2 , while benchmark mass limits on the light scalar and the pseudoscalar Higgs bosons within the MSSM are between 70 GeV/c 2 and 75 GeV/c 2. Other searches cover the charged Higgs boson production and Higgs decays into invisible nal states. Precision tests of the Minimal Standard Model 1] show an excellent agreement of MSM predictions for electroweak observables with electroweak precision data. However, electroweak symmetry breaking requires (at least) one scalar Higgs boson to explain the origin of the particle masses by the Higgs mechanism. Up to now, no experimental evidence for Higgs boson production has been found. Although the MSM makes no direct prediction of the Higgs boson mass, predictions of electroweak data depend on the Higgs mass via radiative corrections. At one loop level, the gauge boson masses aquire loop corrections including top, bottom and Higgs particles, as shown in g. 1 2]. While top-corrections are proportional to M 2 t , Higgs corrections yield only a logarithmic dependence. However, with the precise electroweak data it is possible to restrict the range of the Higgs boson mass. Precision tests of the MSM including all available preliminary electroweak precision data 2] favour a light Higgs boson. The MSM predictions of the electroweak observables 2] have been calculated with the ZFITTER 5.1 package 3], including two loop electroweak corrections. From the 2 of the t shown in g. 2, an upper limit of 212 GeV/c 2 at 95% CL is derived. The preferred Higgs boson mass turns out to be M H = 65 +74 ?39 GeV/c 2 , and the 2 =d:o:f: of the t is 16.0/15, corresponding …