Decay-mode independent searches for new scalar bosons with OPAL

Topological searches for neutral scalar bosons S0 produced in association with a Z0 boson via the Bjorken process e+e- to SZ at centre-of-mass energies of 91GeV and 183-209GeV are described. These searches are based on studies of the recoil mass spectrum of Z to electrons or muons, and on a search for SZ with Z to neutrinos and S to e+e- or photons. They cover the decays of the S into an arbitrary combination of hadrons, leptons, photons and invisible particles as well as the possibility that it might be stable. No indication for a signal is found in the data and upper limits on the cross section of the Bjorken process are calculated. Cross-section limits are given in terms of a scale factor k with respect to the SM cross section for the Higgs-strahlung process e+e- to HZ. These results can be interpreted in general scenarios independently of the decay modes of the S. The examples considered here are the production of a single new scalar particle with a decay width smaller than the detector mass resolution, and for the first time, two scenarios with continuous mass distributions, due to a single very broad state or several states close in mass.