Prospects for observing an invisibly decaying Higgs boson in the ${t \bar t H}$ production at the LHC

Abstract.

The prospects for observing an invisibly decaying Higgs boson in the ${t \bar t H}$ production at LHC are discussed. An isolated lepton, reconstructed hadronic top-quark decay, two identified b-jets and a large missing transverse energy are proposed as the final state signature for event selection. Only the standard model backgrounds are taken into account. It is shown that the $t\bar t Z$, $t \bar t W$, $b \bar b Z$ and $b \bar b W$ backgrounds can individually be suppressed below the signal expectation. The dominant source of background remains the $t \bar t$ production. The key for the observability will be an experimental selection which allows further suppression to be achieved of the contributions from the $t \bar t$ events with one of the top quarks decaying into a tau lepton. Depending on the details of the final analysis, an excess of the signal events above the standard model background of about 10% to 100% can be achieved in the mass range m _H = 100-200 GeV.