Search for `invisible' Higgs signals at LHC via associated production with gauge bosons

Abstract A light Higgs boson with substantial branching ratio into invisible channels can occur in a variety of models with: light neutralinos, spontaneously broken lepton number, radiatively generated neutrino masses, additional singlet scalar(s) and/or right handed neutrinos in the extra dimensions of TeV scale gravity. We study the observability of the WH and ZH modes at LHC with H decaying invisibly, by carrying out a detailed simulation with two event generators ( HERWIG and PYTHIA ) and realistic detector simulations (GETJET and CMSJET). We find that the signal with ‘single lepton plus missing ET’ resulting from WH production suffers from a very large background due to the (off-shell) W ∗ production via the Drell–Yan process. In contrast, the ZH mode provides a clean signal in the ‘dilepton plus missing ET’ channel. By exploiting this second signature, we show that invisible branching ratios of Higgs bosons, BRinv, larger than ∼0.42 (0.70) can be probed at 5σ level for MH=120 (160) GeV, respectively, assuming an accumulated luminosity of L =100 fb −1 .