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

TL;DR

This paper reports on topological searches for new scalar bosons at LEP, setting model-independent upper limits on their production cross sections across various decay modes and mass scenarios, with no signal observed.

Contribution

It introduces decay-mode independent search methods for scalar bosons, including broad and multiple state scenarios, extending previous Higgs searches at LEP.

Findings

No evidence for new scalar bosons was found.

Upper limits on production cross sections were established.

Results are applicable to a wide range of decay modes and mass distributions.

Abstract

This paper describes topological searches for neutral scalar bosons S0 produced in association with a Z0 boson via the Bjorken process e+e- -> S0Z0 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 mu+mu- events on a search for S0Z0 with Z0 -> nunu bar 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-section limits are given in terms of a scale factor k with respect to the Standrad Model cross section for the Higgs-strahlung process e+e- -> H0smZ0. 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.