Search for invisibly decaying Higgs bosons in e+e- -> Zoho production at sqrt(s) 183 - 209 GeV

Abstract A search is performed for Higgs bosonsdecaying into invisiblefinal states, produced in association with a Z 0 bosonin e + e − collisions at energies between 183 and 209 GeV. The search is based on data samples collected by the OPAL detector at LEP corresponding to an integrated luminosity of about 660 pb −1 . The analysis aims to select events containing the hadronic decay productsof the Z 0 bosonand large missing momentum, as expected from Higgs bosondecay into a pair of stable weakly interacting neutral particles, such as the lightest neutralinoin the Minimal Supersymmetric Standard Model. The same analysis is applied to a search for nearly invisible Higgs bosoncascade decays into stable weakly interacting neutral particles. No excess over the expected background from Standard Model processes is observed. Limits on the production of invisiblydecaying Higgs bosonsproduced in association with a Z 0 bosonare derived. Assuming a branching ratio BR ( h 0 → invisible) = 1 , a lower limit of 108.2 GeV is placed on the Higgs bosonmass at the 95% confidence level. Limits on the production of nearly invisiblydecaying Higgs bosonsare also obtained.