A search for Higgs-portal dark matter and new phenomena with monojet signatures in 𝑝𝑝 collisions at √𝑠 = 8 TeV

A search for new phenomena in final states with one or more energetic jets and large missing transverse momentum is presented. An integrated luminosity of 20 fb^1 is collected from √𝑠 = 8 TeV 𝑝𝑝 collisions at the LHC with the ATLAS detector during 2012 operations. Standard Model backgrounds and systematics uncertainties are estimated using a maximum likelihood procedure. The number of events passing this selection criteria is in good agreement with Standard Model expectations. These events are then divided up into three orthogonal signal regions based on the outputs of two Random Forest classifiers trained to classify invisible decays of the Higgs boson produced through the vector boson fusion and Higgs-strahlung production modes. These results are then interpreted in terms of three different Higgs-portal models and translated into upper limits on WIMP-nucleon cross-sections for comparison with direct detection experiments.