Boosting the H → invisibles searches with Z boson polarization

It is argued that, in H -> invisibles searches with Z(ll)H associated production at the LHC, the signal efficiency can be sensibly improved via a detailed study of the Z boson polarization, discriminating between the signal and the dominant-irreducible Z(ll)Z(nu nu)background. We first present a comprehensive polarization study, obtaining the complete set of angular coefficients A(i) in the Collins-Soper reference frame and identifying the dominant phenomenological effects. Then, we show the results for a realistic Monte Carlo study to H -> invisibles, taking the polarization analysis into account. We obtain about 20% improvement in the upper bound for the branching ratio of the Higgs boson to invisible particles, assuming 300 fb(-1) of data at the 13 TeV LHC.