A search for invisible Higgs bosons produced in e+ e- interactions up to s**(1/2) = 189-GeV

Searches for {\mbox{$ {\mathrm H} {\mathrm Z} $}} production d with the Higgs boson decaying into an invisible final state have been performedd the data collected by the DELPHI experimentd up to the centre-of-mass energy of 188.6~{\mbox{$ {\mathrm{GeV}}$}}. d The hadronic and muon pair final states of the d {\mbox{$ {\mathrm Z} $}} d boson were analysed. No signal was found. d Upper limits on the cross-section and the corresponding Higgs boson mass d limits were set d at 95\% confidence level. Combining these results with DELPHI results for the vd a 95\% confidence level Higgs mass lower limit of 92.3~{\mbox{$d {\mathrm{GeV}}$}} was obtained, independentd of the branching ratio into visible and invisible decays.