Limits on a light Higgs boson in e+e− collisions at LEP

Data from e+e− collisions collected with the OPAL detector at LEP have been used to exclude a standard model Higgs boson (H0) with mass below 2mμ. The analysis used 1.2 pb−1 of data taken at centre-of-mass energies between 88.3 and 95.0 GeV to search for the reactions e+e−→Z0H0, (Z0→e+e− or μ+μ−, H0→undetected), e+e−→Z0H0, (Z0→νν, H0→e+e− or γγ). The existence of a minimal standard model H0 with mass in the range 0⩽mH⩽2mμ is excluded at the 95% confidence level. The limit is also valid for standard model extensions with a large branching ratio for the decay of H0 to γγ.