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

TL;DR

This paper reports a search for Higgs bosons decaying into invisible particles in e+e- collisions at energies between 183 and 209 GeV, using data from the OPAL detector at LEP, setting mass limits in the absence of a signal.

Contribution

It presents the first limits on invisibly decaying Higgs bosons in e+e- collisions at LEP energies, including nearly invisible cascade decays, with no observed excess over background.

Findings

No excess observed over Standard Model background.

Lower limit of 108.2 GeV on Higgs mass assuming 100% invisible decay.

Constraints on production of nearly invisible Higgs decays.

Abstract

A search is performed for Higgs bosons decaying into invisible final states, produced in association with a Zo boson in 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 products of the Zo boson and large missing momentum, as expected from Higgs boson decay into a pair of stable weakly interacting neutral particles, such as the lightest neutralino in the Minimal Supersymmetric Standard Model. The same analysis is applied to a search for nearly invisible Higgs boson cascade decays into stable weakly interacting neutral particles. No excess over the expected background from Standard Model processes is observed. Limits on the production of invisibly decaying Higgs bosons produced in association with a Zo boson are derived. Assuming a branching ratio BR(ho->invisible)=1, a lower limit of 108.2 GeV is placed on the Higgs boson mass at the 95% confidence level. Limits on the production of nearly invisibly decaying Higgs bosons are also obtained.