Invisible Final States Research Articles

Searches for invisibly decaying Higgs bosonswith the DELPHI detector at LEP

Searches for HZ production with the Higgs boson decaying into an invisible final state were performed using the data collected by the DELPHI experiment at centre-of-mass energies between 188 GeV and 209 GeV. Both hadronic and leptonic final states of the Z boson were analysed. In addition to the search for a heavy Higgs boson, a dedicated search for a light Higgs boson down to 40 GeV/c(2) was performed. No signal was found. Assuming the Standard Model HZ production cross-section, the mass limit for invisibly decaying Higgs bosons is 112.1 GeV/c(2) at 95% confidence level. An interpretation in the Minimal Supersymmetric extension of the Standard Model (MSSM) and in a Majoron model is also given.

A search for invisible Higgs bosons produced in e+e− interactions at LEP 2 energies

Searches for HZ production with the Higgs boson decaying into an invisible final state have been performed with the data collected by the DELPHI experiment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pair final states of the Z boson were analysed. From the absence of signal, upper limits on the cross-section and the corresponding Higgs boson mass limits were set at 95% confidence level. The results are interpreted as excluded parameter regions in the framework of the minimal supersymmetric standard model and in the simplest Majoron model with one Higgs doublet and one Higgs singlet field.

Missing mass spectra in hadronic events from e+e−collisions at = 161–172 GeV and limits on invisible Higgs decays

Events characterised by large hadronic energy and transverse momentum are selected from the data collected by the L3 detector at LEP at centre-of-mass energies between 161 and 172 GeV, corresponding to an integrated luminosity of 21 $\rm pb^{-1}$. The visible mass and the missing mass distributions of the selected events are consistent with those expected from Standard Model processes. This result is combined with that from data taken at the Z resonance to set an upper limit on the production rate and decay into invisible final states of a non-minimal Higgs boson, as a function of the Higgs mass. Assuming the non-minimal Higgs production cross section to be the same as for the Standard Model Higgs boson and the decay branching fraction into invisible final states to be 100\%, a Higgs mass lower limit of 69.6 GeV is derived at 95\% confidence level.

Search for neutral Higgs boson production through the process e +e − → Z ∗ H 0

The results of the searches for neutral Higgs boson production in the process e +e − → Z ∗ H 0 are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z 0 decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L. These results are also interpreted in the framework of the General Two Doublet Model and limits on the nonstandard Higgs boson production through the process e +e − → Z ∗h 0 are set. A lower limit of 66.7 GeV at 95% C.L. is obtained for the case where the Higgs decays into an invisible final state.

Search for a non-minimal Higgs boson produced in the reaction [formula omitted

A data sample corresponding to 1.23 million hadronic Z decays collected by the ALEPH detector at LEP has been searched for signals of the production of a non-minimal CP-even Higgs boson h in the reaction e+e− → hZ∗. The h decay modes considered were: those of the minimal standard model Higgs boson, with modified branching ratios; decays into a pair of CP-odd Higgs bosons A; and decays into invisible final states. Only one event was found, a very acoplanar e+e− pair which could originate from the standard model background process e+e− → e+e−vv̄. Upper limits for the cross-section of the reaction e+e− → hZ∗ have been derived as a function of mh, the mass of the Higgs boson h. In the case of invisible decays, the 95% CL lower limit on mh is 65 GeV/c2 for a production cross-section equal to that of a minimal standard model Higgs boson. When combined with previous ALEPH results on the reaction e+e− → hA, these cross-section upper limits exclude a domain in the (mhmA) plane of the MSSM such that if invisible h and A decays can be neglected, 95% CL lower limits of 44 and 21 GeV/c2 result for mh and mA, respectively, independent of the other parameters of the model.

Invisible decays of Higgs bosons in supersymmetric models.

We point out that the dominant decay of the light scalar Higgs boson in a supersymmetric model may be into a pair of the lightest neutralinos (assumed to be the lightest supersymmetric particles), which would result in an invisible final state. Thus, in the search at the Stanford Linear Collider and the CERN collider LEP for a Higgs scalar produced in association with a real or virtual Z boson, it is important not to cut out events with significant missing energy recoiling against the Z.