Looking for an invisible Higgs signal at the LHC

Abstract

While the recent discovery of a Higgs-like boson at the LHC is an extremely important and encouraging step towards the discovery of the complete Standard Model (SM), the current information on this state does not rule out possibility of beyond standard model (BSM) physics. In fact the current data can still accommodate reasonably large values of the branching fractions of the Higgs into a channel with ‘invisible’ decay products, such a channel being also well motivated theoretically. In this study we revisit the possibility of detecting the Higgs in this invisible channel for both choices of the LHC energies, 8 and 14 TeV, for two production modes; vector boson fusion (VBF) and associated production (ZH). We perform a comprehensive collider analysis for all the above channels and project the reach of LHC to constrain the invisible decay branching fraction for both 8 and 14 TeV energies. For the ZH case we consider decays of the Z boson into a pair of leptons as well as a bb¯ pair. For the VBF channel the sensitivity is found to be more than 5σ for both the energies up to an invisible branching ratio (Brinv)∼0.80, with luminosities ∼20/30 fb−1. The sensitivity is further extended to values of Brinv∼0.25 for 300 fb−1 at 14 TeV. However the reach is found to be more modest for the ZH mode with leptonic final state; with about 3.5σ for the planned luminosity at 8 TeV, reaching 8σ only for 14 TeV for 50 fb−1. In spite of the much larger branching ratio (BR) of the Z into a bb¯ channel compared to the dilepton case, the former channel, can provide useful reach up to Brinv≳0.75, only for the higher luminosity (300 fb−1) option using both jet-substructure and jet clustering methods.