Search for Charged Higgs Bosons in e+e− Collisions

Sammanfattning: Several extensions to the Standard Model predict the existence of charged Higgs bosons. This thesis describes the search for such a particle using the data collected by the DELPHI detector at the Large Electron Positron (LEP) collider at the European laboratory for particle physics (CERN) in Geneva, Switzerland.In e+e - collisions charged Higgs bosons are predicted to be produced in pairs via an intermediate photon or Z0 boson. In the two Higgs doublet model (2HDM) the production cross section for a pair of charged Higgs bosons depends only on the centre of mass energy of the collision and the mass of the charged Higgs boson.Higgs bosons decay to the heaviest particles kinematically allowed. For a charged Higgs boson with a mass that can be produced at the LEP collider this means either a cs quark pair or a τυt lepton pair. The branching ratio between these decay channels depends on the parameters of the model.No statistically significant signal compatible with a charged Higgs boson was found. Using the predicted production cross sections from the 2HDM the existence of a charged Higgs boson with a mass lower than 73.8 GeV/c2 has been excluded at 95% confidence level independently of the decay branching ratios of the charged Higgs boson.