Searches for HZ production with the Higgs boson decaying into an invisible
final state have been performed with the data collected by the DELPHI exper
iment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pai
r final states of the Z boson were analysed. From the absence of signal, up
per limits on the cross-section and the corresponding Higgs boson mass limi
ts were set at 95% confidence level. The results are interpreted as exclude
d parameter regions in the framework of the minimal supersymmetric standard
model and in the simplest Majoron model with one Higgs doublet and one Hig
gs singlet field. (C) 1999 Elsevier Science B.V. All rights reserved.