Boosting the $H\to$ invisibles searches with $Z$ boson polarization

Abstract

It is argued that, in $H\to$ invisibles searches with $Z(\ell \ell )H$ 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 $Z(\ell \ell )Z(\nu \nu )$ 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 $H\to$ 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 $300{\mathrm{fb}}^{-1}$ of data at the 13 TeV LHC.

Comments: 6 pages, 5 figures