Search for a very light Higgs boson in Z decays

A search has been made for a very light Higgs boson in the processes e+e-→e+e-H and e+e-→μ+μ-H using data collected by ALEPH at the LEP e+e- collider at centre of mass energies close to the Z peak. The mass range between 0 and 57 MeV is unambiguously excluded at the 95% confidence level. If we combine this with our previously published analysis, the complete range from 0 to 24 GeV is excluded at 95% CL. The search is extended to light Higgs bosons of the minimal supersymmetric standard model, with the result that all possibilities of couplings are excluded for Higgs masses below 3 GeV. (orig.)