Looking for Invisibly Decaying Higgs Bosons through the Final State

There are a variety of well motivated extensions of the standard model (SM) with an spontaneously broken global symmetry. This symmetry could be either be lepton number or a combination of family lepton numbers [1, 2]. These models are characterised by a more complex symmetry breaking sector which contain additional Higgs bosons. It is specially interesting for our purposes to consider models where such symmetry is broken at the electroweak scale [3, 4]. In general, these models contain a massless Goldstone boson, called majoron (J), which interacts very weakly with normal matter. In such models, the normal doublet Higgs is expected to have sizeable invisible decay modes to the majoron, due to the strong Higgs majoron coupling. This can have a significant effect on the Higgs phenomenology at LEP II. In particular, the invisible decay could contribute to the signal of two acoplanar jets and missing momentum. This feature of majoron models allows one to strongly constrain the Higgs mass in spite of the occurrence of extra parameters compared to the SM. In particular, the LEP I limit on the predominantly doublet Higgs mass is close to the SM limit irrespective of the decay mode of the Higgs boson [5, 6]. In this work we consider a model containing two Higgs doublets (φ1,2) and a singlet (σ) under the SU(2)L×U(1)Y group. The singlet Higgs field carries a non-vanishing U(1)L charge,