Motivation and detectability of an invisibly decaying Higgs boson at the Fermilab Tevatron - art. no. 035006.

A Higgs boson with a mass below 150 GeV has a total decay width of less tha n 20 MeV into accessible standard model states. This narrow width means tha t the usual branching fractions for such a light Higgs boson are highly sus ceptible to any new particles to which it has unsuppressed couplings. In pa rticular, there are many reasonable and interesting theoretical ideas that naturally imply an invisibly decaying Higgs boson. The motivations include models with light supersymmetric neutralinos, spontaneously broken lepton n umber, radiatively generated neutrino masses, additional singlet scalar(s), or right-handed neutrinos in the extra dimensions of TeV gravity. We discu ss these approaches to model building and their implications for Higgs boso n phenomenology in future Fermilab Tevatron runs. We find, for example, tha t the Tevatron with 30 fb(-1) integrated luminosity can make a 3 sigma obse rvation in the l(+)l(-) + E-T channel for a 125 GeV Higgs bosom that is pro duced with the same strength as the standard model Higgs boson but always d ecays invisibly. We also analyze the b (b) over bar + E-T final state signa l and conclude that it is not as sensitive, but it may assist in excluding the possibility of an invisibly decaying Higgs bosom or enable confirmation of an observed signal in the dilepton channel. We argue that a comprehensi ve Higgs boson search at the Tevatron should include the possibility that t he Higgs boson decays invisibly. [S0556-2821(99)04815-8].