Search for a non-minimal Higgs boson produced in the reaction e+e- → hZ*

A data sample corresponding to 1.23 million hadronic Z decays collected by the ALEPH detector at LEP has been searched for signals of the production of a non-minimal CP-even Higgs boson h in the reaction e+e- → hZ*. The h decay modes considered were: those of the minimal standard model Higgs boson, with modified branching ratios; decays into a pair of CP-odd Higgs bosons A; and decays into invisible final states. Only one event was found, a very acoplanar e+e- pair which could originate from the standard model background process e+e- → e+e-v v ̄. Upper limits for the cross-section of the reaction e+e- → hZ* have been derived as a function of mh, the mass of the Higgs boson h. In the case of invisible decays, the 95% CL lower limit on mh is 65 GeV/c2 for a production cross-section equal to that of a minimal standard model Higgs boson. When combined with previous ALEPH results on the reaction e+e- → hA, these cross-section upper limits exclude a domain in the (mh mA) plane of the MSSM such that if invisible h and A decays can be neglected, 95% CL lower limits of 44 and 21 GeV/c2 result for mh and mA, respectively, independent of the other parameters of the model.