Search for neutral Higgs bosons in the minimal supersymmetric extension of the standard model

A search for the neutral Higgs bosons h0 and A0, predicted by the Minimal Supersymmetric Extension of the Standard Model (MSSM), has been performed by the OPAL Collaboration at LEP. The analysis was based on approximately 75 pb−1 of data taken at centre-of-mass energies in the vicinity of the Z0 resonance. No Higgs boson signals have been detected. Using, in addition, an upper limit on the contribution of non-Standard Model processes to the Z0 boson width, almost the entire MSSM parameter space that can be reached at present LEP energies has been excluded. In particular, at the 95% confidence level, our results imply that$$m_{h^0 } > 44.5$$ GeV/c2 and$$m_{A^0 } > 24.3$$ GeV/c2, for tan β≥1. The sensitivity to this assumption is discussed and the search results are also interpreted in the context of general two-doublet models.