Observing Double Higgs Production at the LHC via Neutrino Feature Engineering in $hh\to b\bar{b}\ell\ellνν$

Abstract: Double Higgs production is challenging even at the High Luminosity LHC. The Standard Model (SM) $hh\to b\bar{b}WW(ZZ)\to b\bar{b}\ell\ell\nu\nu$ has a moderate cross section compared to other decay modes, but its backgrounds, mainly top quark pairs and Drell-Yan production, are overwhelming. In this work, we propose new kinematic features designed to improve the discrimination of double Higgs pairs, in the $b\bar{b}\ell\ell\nu\nu$ channel, with cut-based and multivariate analyses. The new features are built with the neutrinos' momenta solutions obtained from imposing mass constraints when calculating Higgsness and Topness variables. For the SM $hh$ production, we estimate a $3.7\sigma$ statistical significance from an optimized cut-based strategy, improving about 20% over the best estimates of the literature, and $5\sigma$ from a multivariate analysis if systematic uncertainties on the backgrounds are small. The new variables are constructed as ratios of kinematic functions of the particles' momenta, being less prone to systematic errors. We also demonstrate the usefulness of the solutions in reconstructing heavy scalar resonances and other variables of phenomenological importance.