Eur. Phys. J. C 27, 311-329 (2003)
DOI: 10.1140/epjc/s2002-01115-1

Decay-mode independent searches for new scalar bosons with the OPAL detector at LEP

The OPAL Collaboration

(Received: 13 March 2002 / Published online: 19 February 2003 )

Abstract
This paper describes topological searches for neutral scalar bosons S⁰ produced in association with a Z⁰ boson via the Bjorken process e⁺e^- S⁰ Z⁰ at centre-of-mass energies of 91 GeV and 183-209 GeV. These searches are based on studies of the recoil mass spectrum of Z⁰ e⁺e^- and events and on a search for S⁰ Z⁰ with Z⁰ and S⁰ e⁺e^- or photons. They cover the decays of the S⁰ 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-sec tion limits are given in terms of a scale factor k with respect to the Standard Model cross section for the Higgs-strahlung process e⁺e^- Z⁰ .

These results can be interpreted in general scenarios independently of the decay modes of the S⁰ . 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.

© Società Italiana di Fisica, Springer-Verlag 2003